[U-Boot] [PATCH v2] kconfiglib: update to the latest version

Ulf Magnusson ulfalizer at gmail.com
Thu Aug 13 19:55:40 CEST 2015


Corresponds to ba71a0e (Fix _parse_block() 'parent' documentation re.
ifs.) from upstream, just adding the SPDX tag.

Has performance improvements, code cleanup, Python 3 support, and various
small fixes, including the following:

  - Unset user values when loading a zero-byte .config. (5e54e2c)
  - Ignore indented .config assignments. (f8a7510)
  - Do not require $srctree to be set for non-kernel projects. (d56e9c1)
  - Report correct locations in the presence of continuation lines.
    (0cebc87)
---
 tools/buildman/kconfiglib.py | 4226 +++++++++++++++++++-----------------------
 1 file changed, 1940 insertions(+), 2286 deletions(-)

diff --git a/tools/buildman/kconfiglib.py b/tools/buildman/kconfiglib.py
index c662b64..7a47be9 100644
--- a/tools/buildman/kconfiglib.py
+++ b/tools/buildman/kconfiglib.py
@@ -36,57 +36,61 @@ Kconfig-based configuration systems. Features include the following:
 
 For the Linux kernel, scripts are run using
 
- $ make scriptconfig SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
+ $ make scriptconfig [ARCH=<arch>] SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
 
-Running scripts via the 'scriptconfig' target ensures that required environment
-variables (SRCARCH, ARCH, srctree, KERNELVERSION, etc.) are set up correctly.
-Alternative architectures can be specified like for other 'make *config'
-targets:
+Using the 'scriptconfig' target ensures that required environment variables
+(SRCARCH, ARCH, srctree, KERNELVERSION, etc.) are set up correctly.
 
- $ make scriptconfig ARCH=mips SCRIPT=<path to script> [SCRIPT_ARG=<arg>]
-
-The script will receive the name of the Kconfig file to load in sys.argv[1].
-(As of Linux 3.7.0-rc8 this is always "Kconfig" from the kernel top-level
-directory.) If an argument is provided with SCRIPT_ARG, it will appear in
-sys.argv[2].
+Scripts receive the name of the Kconfig file to load in sys.argv[1]. As of
+Linux 4.1.0-rc5, this is always "Kconfig" from the kernel top-level directory.
+If an argument is provided with SCRIPT_ARG, it appears as sys.argv[2].
 
 To get an interactive Python prompt with Kconfiglib preloaded and a Config
-object 'c' created, use
+object 'c' created, run
 
- $ make iscriptconfig [ARCH=<architecture>]
+ $ make iscriptconfig [ARCH=<arch>]
 
-Kconfiglib requires Python 2. For (i)scriptconfig the command to run the Python
-interpreter can be passed in the environment variable PYTHONCMD (defaults to
-'python'; PyPy works too and is a bit faster).
+Kconfiglib supports both Python 2 and Python 3. For (i)scriptconfig, the Python
+interpreter to use can be passed in PYTHONCMD, which defaults to 'python'. PyPy
+works well too, and might give a nice speedup for long-running jobs.
 
-Look in the examples/ subdirectory for examples, which can be run with e.g.
+The examples/ directory contains short example scripts, which can be run with
+e.g.
 
  $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
 
 or
 
- $ make scriptconfig SCRIPT=Kconfiglib/examples/help_grep.py SCRIPT_ARG="kernel"
+ $ make scriptconfig SCRIPT=Kconfiglib/examples/help_grep.py SCRIPT_ARG=kernel
 
-Look in testsuite.py for the test suite.
+testsuite.py contains the test suite. See the top of the script for how to run
+it.
 
 Credits: Written by Ulf "Ulfalizer" Magnusson
 
-Send bug reports, suggestions and other feedback to kconfiglib at gmail.com .
-Don't wrestle with internal APIs. Tell me what you need and I might add it in a
-safe way as a client API instead."""
-
-# If you have Psyco installed (32-bit installations, Python <= 2.6 only),
-# setting this to True (right here, not at runtime) might give a nice speedup.
-# (22% faster for parsing arch/x86/Kconfig and 58% faster for evaluating all
-# symbols in it without a .config on my Core Duo.)
-use_psyco = False
+Send bug reports, suggestions and other feedback to ulfalizer a.t Google's
+email service. Don't wrestle with internal APIs. Tell me what you need and I
+might add it in a safe way as a client API instead."""
 
 import os
 import re
-import string
 import sys
 
-class Config():
+# File layout:
+#
+# Public classes
+# Public functions
+# Internal classes
+# Internal functions
+# Internal global constants
+
+# Line length: 79 columns
+
+#
+# Public classes
+#
+
+class Config(object):
 
     """Represents a Kconfig configuration, e.g. for i386 or ARM. This is the
     set of symbols and other items appearing in the configuration together with
@@ -97,46 +101,46 @@ class Config():
     # Public interface
     #
 
-    def __init__(self,
-                 filename = "Kconfig",
-                 base_dir = "$srctree",
-                 print_warnings = True,
-                 print_undef_assign = False):
+    def __init__(self, filename="Kconfig", base_dir=None, print_warnings=True,
+                 print_undef_assign=False):
         """Creates a new Config object, representing a Kconfig configuration.
         Raises Kconfig_Syntax_Error on syntax errors.
 
-        filename (default: "Kconfig") -- The base Kconfig file of the
-                 configuration. For the Linux kernel, this should usually be be
-                 "Kconfig" from the top-level directory, as environment
-                 variables will make sure the right Kconfig is included from
-                 there (usually arch/<architecture>/Kconfig). If you are using
-                 kconfiglib via 'make scriptconfig' the filename of the
-                 correct Kconfig will be in sys.argv[1].
-
-        base_dir (default: "$srctree") -- The base directory relative to which
-                'source' statements within Kconfig files will work. For the
-                Linux kernel this should be the top-level directory of the
-                kernel tree. $-references to environment variables will be
-                expanded.
-
-                The environment variable 'srctree' is set by the Linux makefiles
-                to the top-level kernel directory. A default of "." would not
-                work if an alternative build directory is used.
-
-        print_warnings (default: True) -- Set to True if warnings related to
-                       this configuration should be printed to stderr. This can
-                       be changed later with Config.set_print_warnings(). It is
-                       provided as a constructor argument since warnings might
-                       be generated during parsing.
-
-        print_undef_assign (default: False) -- Set to True if informational
-                           messages related to assignments to undefined symbols
-                           should be printed to stderr for this configuration.
-                           Can be changed later with
-                           Config.set_print_undef_assign()."""
+        filename (default: "Kconfig"): The base Kconfig file of the
+           configuration. For the Linux kernel, you'll probably want "Kconfig"
+           from the top-level directory, as environment variables will make
+           sure the right Kconfig is included from there
+           (arch/<architecture>/Kconfig). If you are using Kconfiglib via 'make
+           scriptconfig', the filename of the base base Kconfig file will be in
+           sys.argv[1].
+
+        base_dir (default: None): The base directory relative to which 'source'
+           statements within Kconfig files will work. For the Linux kernel this
+           should be the top-level directory of the kernel tree. $-references
+           to existing environment variables will be expanded.
+
+           If None (the default), the environment variable 'srctree' will be
+           used if set, and the current directory otherwise. 'srctree' is set
+           by the Linux makefiles to the top-level kernel directory. A default
+           of "." would not work with an alternative build directory.
+
+        print_warnings (default: True): Set to True if warnings related to this
+           configuration should be printed to stderr. This can be changed later
+           with Config.set_print_warnings(). It is provided as a constructor
+           argument since warnings might be generated during parsing.
+
+        print_undef_assign (default: False): Set to True if informational
+           messages related to assignments to undefined symbols should be
+           printed to stderr for this configuration. Can be changed later with
+           Config.set_print_undef_assign()."""
 
         # The set of all symbols, indexed by name (a string)
         self.syms = {}
+        # Python 2/3 compatibility hack. This is the only one needed.
+        if sys.version_info[0] >= 3:
+            self.syms_iter = self.syms.values
+        else:
+            self.syms_iter = self.syms.itervalues
 
         # The set of all defined symbols in the configuration in the order they
         # appear in the Kconfig files. This excludes the special symbols n, m,
@@ -147,14 +151,19 @@ class Config():
         # by name (a string)
         self.named_choices = {}
 
-        def register_special_symbol(type, name, value):
+        # Lists containing all choices, menus and comments in the configuration
+        self.choices = []
+        self.menus = []
+        self.comments = []
+
+        def register_special_symbol(type_, name, val):
             sym = Symbol()
             sym.is_special_ = True
             sym.is_defined_ = True
             sym.config = self
             sym.name = name
-            sym.type = type
-            sym.cached_value = value
+            sym.type = type_
+            sym.cached_val = val
             self.syms[name] = sym
             return sym
 
@@ -163,7 +172,6 @@ class Config():
         self.n = register_special_symbol(TRISTATE, "n", "n")
         self.m = register_special_symbol(TRISTATE, "m", "m")
         self.y = register_special_symbol(TRISTATE, "y", "y")
-
         # DEFCONFIG_LIST uses this
         register_special_symbol(STRING, "UNAME_RELEASE", os.uname()[2])
 
@@ -172,7 +180,7 @@ class Config():
         self.defconfig_sym = None
 
         # See Symbol.get_(src)arch()
-        self.arch    = os.environ.get("ARCH")
+        self.arch = os.environ.get("ARCH")
         self.srcarch = os.environ.get("SRCARCH")
 
         # See Config.__init__(). We need this for get_defconfig_filename().
@@ -181,26 +189,22 @@ class Config():
             self.srctree = "."
 
         self.filename = filename
-        self.base_dir = _strip_trailing_slash(os.path.expandvars(base_dir))
+        if base_dir is None:
+            self.base_dir = self.srctree
+        else:
+            self.base_dir = os.path.expandvars(base_dir)
 
         # The 'mainmenu' text
         self.mainmenu_text = None
 
         # The filename of the most recently loaded .config file
         self.config_filename = None
-
         # The textual header of the most recently loaded .config, uncommented
         self.config_header = None
 
         self.print_warnings = print_warnings
         self.print_undef_assign = print_undef_assign
 
-        # Lists containing all choices, menus and comments in the configuration
-
-        self.choices = []
-        self.menus = []
-        self.comments = []
-
         # For parsing routines that stop when finding a line belonging to a
         # different construct, these holds that line and the tokenized version
         # of that line. The purpose is to avoid having to re-tokenize the line,
@@ -210,11 +214,11 @@ class Config():
         self.end_line_tokens = None
 
         # See the comment in _parse_expr().
-        self.parse_expr_cur_sym_or_choice = None
-        self.parse_expr_line = None
-        self.parse_expr_filename = None
-        self.parse_expr_linenr = None
-        self.parse_expr_transform_m = None
+        self._cur_item = None
+        self._line = None
+        self._filename = None
+        self._linenr = None
+        self._transform_m = None
 
         # Parse the Kconfig files
         self.top_block = self._parse_file(filename, None, None, None)
@@ -222,169 +226,6 @@ class Config():
         # Build Symbol.dep for all symbols
         self._build_dep()
 
-    def load_config(self, filename, replace = True):
-        """Loads symbol values from a file in the familiar .config format.
-           Equivalent to calling Symbol.set_user_value() to set each of the
-           values.
-
-           filename -- The .config file to load. $-references to environment
-                       variables will be expanded. For scripts to work even
-                       when an alternative build directory is used with the
-                       Linux kernel, you need to refer to the top-level kernel
-                       directory with "$srctree".
-
-           replace (default: True) -- True if the configuration should replace
-                   the old configuration; False if it should add to it."""
-
-        def warn_override(filename, linenr, name, old_user_val, new_user_val):
-            self._warn("overriding the value of {0}. "
-                       'Old value: "{1}", new value: "{2}".'
-                        .format(name, old_user_val, new_user_val),
-                       filename,
-                       linenr)
-
-        filename = os.path.expandvars(filename)
-
-        # Put this first so that a missing file doesn't screw up our state
-        line_feeder = _FileFeed(_get_lines(filename), filename)
-
-        self.config_filename = filename
-
-        # Invalidate everything. This is usually faster than finding the
-        # minimal set of symbols that needs to be invalidated, as nearly all
-        # symbols will tend to be affected anyway.
-        if replace:
-            self.unset_user_values()
-        else:
-            self._invalidate_all()
-
-        # Read header
-
-        self.config_header = None
-
-        def is_header_line(line):
-            return line.startswith("#") and \
-                   not unset_re.match(line)
-
-        first_line = line_feeder.get_next()
-
-        if first_line is None:
-            return
-
-        if not is_header_line(first_line):
-            line_feeder.go_back()
-        else:
-            self.config_header = first_line[1:]
-
-            # Read remaining header lines
-            while 1:
-                line = line_feeder.get_next()
-
-                if line is None:
-                    break
-
-                if not is_header_line(line):
-                    line_feeder.go_back()
-                    break
-
-                self.config_header += line[1:]
-
-            # Remove trailing newline
-            if self.config_header.endswith("\n"):
-                self.config_header = self.config_header[:-1]
-
-        # Read assignments
-
-        filename = line_feeder.get_filename()
-
-        while 1:
-            line = line_feeder.get_next()
-            if line is None:
-                return
-
-            linenr = line_feeder.get_linenr()
-
-            line = line.strip()
-
-            set_re_match = set_re.match(line)
-            if set_re_match:
-                name, val = set_re_match.groups()
-                # The unescaping producedure below should be safe since " can
-                # only appear as \" inside the string
-                val = _strip_quotes(val, line, filename, linenr)\
-                      .replace('\\"', '"').replace("\\\\", "\\")
-                if name in self.syms:
-                    sym = self.syms[name]
-
-                    old_user_val = sym.user_val
-                    if old_user_val is not None:
-                        warn_override(filename, linenr, name, old_user_val, val)
-
-                    if sym.is_choice_symbol_:
-                        user_mode = sym.parent.user_mode
-                        if user_mode is not None and user_mode != val:
-                            self._warn("assignment to {0} changes mode of containing "
-                                       'choice from "{1}" to "{2}".'
-                                       .format(name, val, user_mode),
-                                       filename,
-                                       linenr)
-
-                    sym._set_user_value_no_invalidate(val, True)
-
-                else:
-                    self._undef_assign('attempt to assign the value "{0}" to the '
-                                       "undefined symbol {1}."
-                                       .format(val, name),
-                                       filename,
-                                       linenr)
-
-            else:
-                unset_re_match = unset_re.match(line)
-                if unset_re_match:
-                    name = unset_re_match.group(1)
-                    if name in self.syms:
-                        sym = self.syms[name]
-
-                        old_user_val = sym.user_val
-                        if old_user_val is not None:
-                            warn_override(filename, linenr, name, old_user_val, "n")
-
-                        sym._set_user_value_no_invalidate("n", True)
-
-    def write_config(self, filename, header = None):
-        """Writes out symbol values in the familiar .config format.
-
-           filename -- The filename under which to save the configuration.
-
-           header (default: None) -- A textual header that will appear at the
-                  beginning of the file, with each line commented out
-                  automatically. None means no header."""
-
-        # already_written is set when _make_conf() is called on a symbol, so
-        # that symbols defined in multiple locations only get one entry in the
-        # .config. We need to reset it prior to writing out a new .config.
-        for sym in self.syms.itervalues():
-            sym.already_written = False
-
-        with open(filename, "w") as f:
-            # Write header
-            if header is not None:
-                f.write(_comment(header))
-                f.write("\n")
-
-            # Write configuration.
-            # (You'd think passing a list around to all the nodes and appending
-            # to it to avoid copying would be faster, but it's actually a lot
-            # slower with PyPy, and about as fast with Python. Passing the file
-            # around is slower too.)
-            f.write("\n".join(self.top_block._make_conf()))
-            f.write("\n")
-
-    def get_kconfig_filename(self):
-        """Returns the name of the (base) kconfig file this configuration was
-        loaded from."""
-        return self.filename
-
     def get_arch(self):
         """Returns the value the environment variable ARCH had at the time the
         Config instance was created, or None if ARCH was not set. For the
@@ -395,8 +236,8 @@ class Config():
     def get_srcarch(self):
         """Returns the value the environment variable SRCARCH had at the time
         the Config instance was created, or None if SRCARCH was not set. For
-        the kernel, this corresponds to the arch/ subdirectory containing
-        architecture-specific source code."""
+        the kernel, this corresponds to the particular arch/ subdirectory
+        containing architecture-specific code."""
         return self.srcarch
 
     def get_srctree(self):
@@ -406,11 +247,33 @@ class Config():
         in a separate directory."""
         return self.srctree
 
+    def get_base_dir(self):
+        """Returns the base directory relative to which 'source' statements
+        will work, passed as an argument to Config.__init__()."""
+        return self.base_dir
+
+    def get_kconfig_filename(self):
+        """Returns the name of the (base) kconfig file this configuration was
+        loaded from."""
+        return self.filename
+
     def get_config_filename(self):
-        """Returns the name of the most recently loaded configuration file, or
-        None if no configuration has been loaded."""
+        """Returns the filename of the most recently loaded configuration file,
+        or None if no configuration has been loaded."""
         return self.config_filename
 
+    def get_config_header(self):
+        """Returns the (uncommented) textual header of the .config file most
+        recently loaded with load_config(). Returns None if no .config file has
+        been loaded or if the most recently loaded .config file has no header.
+        The header consists of all lines up to but not including the first line
+        that either
+
+        1. Does not start with "#"
+        2. Has the form "# CONFIG_FOO is not set."
+        """
+        return self.config_header
+
     def get_mainmenu_text(self):
         """Returns the text of the 'mainmenu' statement (with $-references to
         symbols replaced by symbol values), or None if the configuration has no
@@ -431,30 +294,26 @@ class Config():
         directory before looking in the current directory; see
         Config.__init__().
 
-        WARNING: A wart here is that scripts/kconfig/Makefile sometimes uses the
-        --defconfig=<defconfig> option when calling the C implementation of e.g.
-        'make defconfig'. This option overrides the 'option defconfig_list'
-        symbol, meaning the result from get_defconfig_filename() might not
-        match what 'make defconfig' would use. That probably ought to be worked
-        around somehow, so that this function always gives the "expected"
-        result."""
-
+        WARNING: A wart here is that scripts/kconfig/Makefile sometimes uses
+        the --defconfig=<defconfig> option when calling the C implementation of
+        e.g. 'make defconfig'. This option overrides the 'option
+        defconfig_list' symbol, meaning the result from
+        get_defconfig_filename() might not match what 'make defconfig' would
+        use. That probably ought to be worked around somehow, so that this
+        function always gives the "expected" result."""
         if self.defconfig_sym is None:
             return None
-
-        for (filename, cond_expr) in self.defconfig_sym.def_exprs:
+        for filename, cond_expr in self.defconfig_sym.def_exprs:
             if self._eval_expr(cond_expr) == "y":
                 filename = self._expand_sym_refs(filename)
-
                 # We first look in $srctree. os.path.join() won't work here as
                 # an absolute path in filename would override $srctree.
-                srctree_filename = os.path.normpath(self.srctree + "/" + filename)
+                srctree_filename = os.path.normpath(self.srctree + "/" +
+                                                    filename)
                 if os.path.exists(srctree_filename):
                     return srctree_filename
-
                 if os.path.exists(filename):
                     return filename
-
         return None
 
     def get_symbol(self, name):
@@ -464,14 +323,12 @@ class Config():
         KeyError if the symbol does not exist."""
         return self.syms.get(name)
 
-    def get_top_level_items(self):
-        """Returns a list containing the items (symbols, menus, choice
-        statements and comments) at the top level of the configuration -- that
-        is, all items that do not appear within a menu or choice. The items
-        appear in the same order as within the configuration."""
-        return self.top_block.get_items()
+    def __getitem__(self, name):
+        """Returns the symbol with name 'name'. Raises KeyError if the symbol
+        does not appear in the configuration."""
+        return self.syms[name]
 
-    def get_symbols(self, all_symbols = True):
+    def get_symbols(self, all_symbols=True):
         """Returns a list of symbols from the configuration. An alternative for
         iterating over all defined symbols (in the order of definition) is
 
@@ -483,13 +340,26 @@ class Config():
         for sym in config.get_symbols(False):
             ...
 
-        all_symbols (default: True) -- If True, all symbols - including special
-                    and undefined symbols - will be included in the result, in
-                    an undefined order. If False, only symbols actually defined
-                    and not merely referred to in the configuration will be
-                    included in the result, and will appear in the order that
-                    they are defined within the Kconfig configuration files."""
-        return self.syms.values() if all_symbols else self.kconfig_syms
+        all_symbols (default: True): If True, all symbols -- including special
+           and undefined symbols -- will be included in the result, in an
+           undefined order. If False, only symbols actually defined and not
+           merely referred to in the configuration will be included in the
+           result, and will appear in the order that they are defined within
+           the Kconfig configuration files."""
+        return list(self.syms.values()) if all_symbols else self.kconfig_syms
+
+    def __iter__(self):
+        """Convenience function for iterating over the set of all defined
+        symbols in the configuration, used like
+
+        for sym in conf:
+            ...
+
+        The iteration happens in the order of definition within the Kconfig
+        configuration files. Symbols only referred to but not defined will not
+        be included, nor will the special symbols n, m, and y. If you want to
+        include such symbols as well, see config.get_symbols()."""
+        return iter(self.kconfig_syms)
 
     def get_choices(self):
         """Returns a list containing all choice statements in the
@@ -506,6 +376,158 @@ class Config():
         order they appear in the Kconfig files."""
         return self.comments
 
+    def get_top_level_items(self):
+        """Returns a list containing the items (symbols, menus, choices, and
+        comments) at the top level of the configuration -- that is, all items
+        that do not appear within a menu or choice. The items appear in the
+        same order as within the configuration."""
+        return self.top_block
+
+    def load_config(self, filename, replace=True):
+        """Loads symbol values from a file in the familiar .config format.
+        Equivalent to calling Symbol.set_user_value() to set each of the
+        values.
+
+        "# CONFIG_FOO is not set" within a .config file is treated specially
+        and sets the user value of FOO to 'n'. The C implementation works the
+        same way.
+
+        filename: The .config file to load. $-references to existing
+          environment variables will be expanded. For scripts to work even when
+          an alternative build directory is used with the Linux kernel, you
+          need to refer to the top-level kernel directory with "$srctree".
+
+        replace (default: True): True if the configuration should replace the
+           old configuration; False if it should add to it."""
+
+        # Put this first so that a missing file doesn't screw up our state
+        filename = os.path.expandvars(filename)
+        line_feeder = _FileFeed(filename)
+
+        self.config_filename = filename
+
+        #
+        # Read header
+        #
+
+        def is_header_line(line):
+            return line is not None and line.startswith("#") and \
+                   not _unset_re_match(line)
+
+        self.config_header = None
+
+        line = line_feeder.peek_next()
+        if is_header_line(line):
+            self.config_header = ""
+            while is_header_line(line_feeder.peek_next()):
+                self.config_header += line_feeder.get_next()[1:]
+            # Remove trailing newline
+            if self.config_header.endswith("\n"):
+                self.config_header = self.config_header[:-1]
+
+        #
+        # Read assignments. Hotspot for some workloads.
+        #
+
+        def warn_override(filename, linenr, name, old_user_val, new_user_val):
+            self._warn('overriding the value of {0}. '
+                       'Old value: "{1}", new value: "{2}".'
+                       .format(name, old_user_val, new_user_val),
+                       filename, linenr)
+
+        # Invalidate everything to keep things simple. It might be possible to
+        # improve performance for the case where multiple configurations are
+        # loaded by only invalidating a symbol (and its dependent symbols) if
+        # the new user value differs from the old. One complication would be
+        # that symbols not mentioned in the .config must lose their user value
+        # when replace = True, which is the usual case.
+        if replace:
+            self.unset_user_values()
+        else:
+            self._invalidate_all()
+
+        while 1:
+            line = line_feeder.get_next()
+            if line is None:
+                return
+
+            line = line.rstrip()
+
+            set_match = _set_re_match(line)
+            if set_match:
+                name, val = set_match.groups()
+
+                if val.startswith('"'):
+                    if len(val) < 2 or val[-1] != '"':
+                        _parse_error(line, "malformed string literal",
+                                     line_feeder.filename, line_feeder.linenr)
+                    # Strip quotes and remove escapings. The unescaping
+                    # procedure should be safe since " can only appear as \"
+                    # inside the string.
+                    val = val[1:-1].replace('\\"', '"').replace("\\\\", "\\")
+
+                if name in self.syms:
+                    sym = self.syms[name]
+                    if sym.user_val is not None:
+                        warn_override(line_feeder.filename, line_feeder.linenr,
+                                      name, sym.user_val, val)
+
+                    if sym.is_choice_sym:
+                        user_mode = sym.parent.user_mode
+                        if user_mode is not None and user_mode != val:
+                            self._warn("assignment to {0} changes mode of "
+                                       'containing choice from "{1}" to "{2}".'
+                                       .format(name, val, user_mode),
+                                       line_feeder.filename,
+                                       line_feeder.linenr)
+
+                    sym._set_user_value_no_invalidate(val, True)
+                else:
+                    if self.print_undef_assign:
+                        _stderr_msg('note: attempt to assign the value "{0}" '
+                                    "to the undefined symbol {1}."
+                                    .format(val, name),
+                                    line_feeder.filename, line_feeder.linenr)
+            else:
+                unset_match = _unset_re_match(line)
+                if unset_match:
+                    name = unset_match.group(1)
+                    if name in self.syms:
+                        sym = self.syms[name]
+                        if sym.user_val is not None:
+                            warn_override(line_feeder.filename,
+                                          line_feeder.linenr,
+                                          name, sym.user_val, "n")
+
+                        sym._set_user_value_no_invalidate("n", True)
+
+    def write_config(self, filename, header=None):
+        """Writes out symbol values in the familiar .config format.
+
+        Kconfiglib makes sure the format matches what the C implementation
+        would generate, down to whitespace. This eases testing.
+
+        filename: The filename under which to save the configuration.
+
+        header (default: None): A textual header that will appear at the
+           beginning of the file, with each line commented out automatically.
+           None means no header."""
+
+        for sym in self.syms_iter():
+            sym.already_written = False
+
+        with open(filename, "w") as f:
+            # Write header
+            if header is not None:
+                f.write(_comment(header))
+                f.write("\n")
+
+            # Build and write configuration
+            conf_strings = []
+            _make_block_conf(self.top_block, conf_strings.append)
+            f.write("\n".join(conf_strings))
+            f.write("\n")
+
     def eval(self, s):
         """Returns the value of the expression 's' -- where 's' is represented
         as a string -- in the context of the configuration. Raises
@@ -521,478 +543,125 @@ class Config():
         conditional expressions in the configuration as well as in the C
         implementation. "m" and m are rewritten as '"m" && MODULES' and 'm &&
         MODULES', respectively, and a result of "m" will get promoted to "y" if
-        we're running without modules."""
+        we're running without modules.
+
+        Syntax checking is somewhat lax, partly to be compatible with lax
+        parsing in the C implementation."""
         return self._eval_expr(self._parse_expr(self._tokenize(s, True), # Feed
-                                                None, # Current symbol or choice
+                                                None, # Current symbol/choice
                                                 s))   # line
 
-    def get_config_header(self):
-        """Returns the (uncommented) textual header of the .config file most
-        recently loaded with load_config(). Returns None if no .config file has
-        been loaded or if the most recently loaded .config file has no header.
-        The header comprises all lines up to but not including the first line
-        that either
-
-        1. Does not start with "#"
-        2. Has the form "# CONFIG_FOO is not set."
-        """
-        return self.config_header
-
-    def get_base_dir(self):
-        """Returns the base directory relative to which 'source' statements
-        will work, passed as an argument to Config.__init__()."""
-        return self.base_dir
+    def unset_user_values(self):
+        """Resets the values of all symbols, as if Config.load_config() or
+        Symbol.set_user_value() had never been called."""
+        for sym in self.syms_iter():
+            sym._unset_user_value_no_recursive_invalidate()
 
     def set_print_warnings(self, print_warnings):
         """Determines whether warnings related to this configuration (for
         things like attempting to assign illegal values to symbols with
         Symbol.set_user_value()) should be printed to stderr.
 
-        print_warnings -- True if warnings should be
-                          printed, otherwise False."""
+        print_warnings: True if warnings should be printed."""
         self.print_warnings = print_warnings
 
     def set_print_undef_assign(self, print_undef_assign):
         """Determines whether informational messages related to assignments to
         undefined symbols should be printed to stderr for this configuration.
 
-        print_undef_assign -- If True, such messages will be printed."""
+        print_undef_assign: If True, such messages will be printed."""
         self.print_undef_assign = print_undef_assign
 
-    def __getitem__(self, key):
-        """Returns the symbol with name 'name'. Raises KeyError if the symbol
-        does not appear in the configuration."""
-        return self.syms[key]
-
-    def __iter__(self):
-        """Convenience function for iterating over the set of all defined
-        symbols in the configuration, used like
-
-        for sym in conf:
-            ...
-
-        The iteration happens in the order of definition within the Kconfig
-        configuration files. Symbols only referred to but not defined will not
-        be included, nor will the special symbols n, m, and y. If you want to
-        include such symbols as well, see config.get_symbols()."""
-        return iter(self.kconfig_syms)
-
-    def unset_user_values(self):
-        """Resets the values of all symbols, as if Config.load_config() or
-        Symbol.set_user_value() had never been called."""
-        for sym in self.syms.itervalues():
-            sym._unset_user_value_no_recursive_invalidate()
-
-    def __str__(self):
-        """Returns a string containing various information about the Config."""
-        return _sep_lines("Configuration",
-                          "File                                   : " + self.filename,
-                          "Base directory                         : " + self.base_dir,
-                          "Value of $ARCH at creation time        : " +
-                            ("(not set)" if self.arch is None else self.arch),
-                          "Value of $SRCARCH at creation time     : " +
-                            ("(not set)" if self.srcarch is None else self.srcarch),
-                          "Source tree (derived from $srctree;",
-                          "defaults to '.' if $srctree isn't set) : " + self.srctree,
-                          "Most recently loaded .config           : " +
-                            ("(no .config loaded)" if self.config_filename is None else
-                             self.config_filename),
-                          "Print warnings                         : " +
-                            bool_str[self.print_warnings],
-                          "Print assignments to undefined symbols : " +
-                            bool_str[self.print_undef_assign])
-
+    def __str__(self):
+        """Returns a string containing various information about the Config."""
+        return _lines("Configuration",
+                      "File                                   : " +
+                        self.filename,
+                      "Base directory                         : " +
+                        self.base_dir,
+                      "Value of $ARCH at creation time        : " +
+                        ("(not set)" if self.arch is None else self.arch),
+                      "Value of $SRCARCH at creation time     : " +
+                        ("(not set)" if self.srcarch is None else
+                                        self.srcarch),
+                      "Source tree (derived from $srctree;",
+                      "defaults to '.' if $srctree isn't set) : " +
+                        self.srctree,
+                      "Most recently loaded .config           : " +
+                        ("(no .config loaded)"
+                          if self.config_filename is None else
+                             self.config_filename),
+                      "Print warnings                         : " +
+                        BOOL_STR[self.print_warnings],
+                      "Print assignments to undefined symbols : " +
+                        BOOL_STR[self.print_undef_assign])
 
     #
     # Private methods
     #
 
-    def _invalidate_all(self):
-        for sym in self.syms.itervalues():
-            sym._invalidate()
-
-    def _tokenize(self,
-                  s,
-                  for_eval = False,
-                  filename = None,
-                  linenr = None):
-        """Returns a _Feed instance containing tokens derived from the string
-        's'. Registers any new symbols encountered (via _sym_lookup()).
-
-        (I experimented with a pure regular expression implementation, but it
-        came out slower, less readable, and wouldn't have been as flexible.)
-
-        for_eval -- True when parsing an expression for a call to
-                    Config.eval(), in which case we should not treat the first
-                    token specially nor register new symbols."""
-        s = s.lstrip()
-        if s == "" or s[0] == "#":
-            return _Feed([])
-
-        if for_eval:
-            i = 0 # The current index in the string being tokenized
-            previous = None # The previous token seen
-            tokens = []
-        else:
-            # The initial word on a line is parsed specially. Let
-            # command_chars = [A-Za-z0-9_]. Then
-            #  - leading non-command_chars characters on the line are ignored, and
-            #  - the first token consists the following one or more command_chars
-            #    characters.
-            # This is why things like "----help--" are accepted.
-
-            initial_token_match = initial_token_re.match(s)
-            if initial_token_match is None:
-                return _Feed([])
-            # The current index in the string being tokenized
-            i = initial_token_match.end()
-
-            keyword = keywords.get(initial_token_match.group(1))
-            if keyword is None:
-                # We expect a keyword as the first token
-                _tokenization_error(s, len(s), filename, linenr)
-            if keyword == T_HELP:
-                # Avoid junk after "help", e.g. "---", being registered as a
-                # symbol
-                return _Feed([T_HELP])
-            tokens = [keyword]
-            previous = keyword
-
-        # _tokenize() is a hotspot during parsing, and this speeds things up a
-        # bit
-        strlen = len(s)
-        append = tokens.append
-
-        # Main tokenization loop. (Handles tokens past the first one.)
-        while i < strlen:
-            # Test for an identifier/keyword preceded by whitespace first; this
-            # is the most common case.
-            id_keyword_match = id_keyword_re.match(s, i)
-            if id_keyword_match:
-                # We have an identifier or keyword. The above also stripped any
-                # whitespace for us.
-                name = id_keyword_match.group(1)
-                # Jump past it
-                i = id_keyword_match.end()
-
-                # Keyword?
-                keyword = keywords.get(name)
-                if keyword is not None:
-                    append(keyword)
-                # What would ordinarily be considered a name is treated as a
-                # string after certain tokens.
-                elif previous in string_lex:
-                    append(name)
-                else:
-                    # We're dealing with a symbol. _sym_lookup() will take care
-                    # of allocating a new Symbol instance if it's the first
-                    # time we see it.
-                    sym = self._sym_lookup(name, not for_eval)
-
-                    if previous == T_CONFIG or previous == T_MENUCONFIG:
-                        # If the previous token is T_(MENU)CONFIG
-                        # ("(menu)config"), we're tokenizing the first line of
-                        # a symbol definition, and should remember this as a
-                        # location where the symbol is defined.
-                        sym.def_locations.append((filename, linenr))
-                    else:
-                        # Otherwise, it's a reference to the symbol
-                        sym.ref_locations.append((filename, linenr))
-
-                    append(sym)
-
-            else:
-                # This restrips whitespace that could have been stripped in the
-                # regex above, but it's worth it since identifiers/keywords are
-                # more common
-                s = s[i:].lstrip()
-                if s == "":
-                    break
-                strlen = len(s)
-                i = 0
-                c = s[0]
-
-                # String literal (constant symbol)
-                if c == '"' or c == "'":
-                    i += 1
-
-                    if "\\" in s:
-                        # Slow path: This could probably be sped up, but it's a
-                        # very unusual case anyway.
-                        quote = c
-                        value = ""
-                        while 1:
-                            if i >= strlen:
-                                _tokenization_error(s, strlen, filename,
-                                                    linenr)
-                            c = s[i]
-                            if c == quote:
-                                break
-                            if c == "\\":
-                                if i + 1 >= strlen:
-                                    _tokenization_error(s, strlen, filename,
-                                                        linenr)
-                                value += s[i + 1]
-                                i += 2
-                            else:
-                                value += c
-                                i += 1
-                        i += 1
-                        append(value)
-                    else:
-                        # Fast path: If the string contains no backslashes (almost
-                        # always) we can simply look for the matching quote.
-                        end = s.find(c, i)
-                        if end == -1:
-                            _tokenization_error(s, strlen, filename, linenr)
-                        append(s[i:end])
-                        i = end + 1
-
-                elif c == "&":
-                    if i + 1 >= strlen:
-                        # Invalid characters are ignored
-                        continue
-                    if s[i + 1] != "&":
-                        # Invalid characters are ignored
-                        i += 1
-                        continue
-                    append(T_AND)
-                    i += 2
-
-                elif c == "|":
-                    if i + 1 >= strlen:
-                        # Invalid characters are ignored
-                        continue
-                    if s[i + 1] != "|":
-                        # Invalid characters are ignored
-                        i += 1
-                        continue
-                    append(T_OR)
-                    i += 2
-
-                elif c == "!":
-                    if i + 1 >= strlen:
-                        _tokenization_error(s, strlen, filename, linenr)
-                    if s[i + 1] == "=":
-                        append(T_UNEQUAL)
-                        i += 2
-                    else:
-                        append(T_NOT)
-                        i += 1
-
-                elif c == "=":
-                    append(T_EQUAL)
-                    i += 1
-
-                elif c == "(":
-                    append(T_OPEN_PAREN)
-                    i += 1
-
-                elif c == ")":
-                    append(T_CLOSE_PAREN)
-                    i += 1
-
-                elif c == "#":
-                    break
-
-                else:
-                    # Invalid characters are ignored
-                    i += 1
-                    continue
-
-            previous = tokens[-1]
-
-        return _Feed(tokens)
-
     #
-    # Parsing
-    #
-
-    # Expression grammar:
+    # Kconfig parsing
     #
-    # <expr> -> <symbol>
-    #           <symbol> '=' <symbol>
-    #           <symbol> '!=' <symbol>
-    #           '(' <expr> ')'
-    #           '!' <expr>
-    #           <expr> '&&' <expr>
-    #           <expr> '||' <expr>
-
-    def _parse_expr(self,
-                    feed,
-                    cur_sym_or_choice,
-                    line,
-                    filename = None,
-                    linenr = None,
-                    transform_m = True):
-        """Parse an expression from the tokens in 'feed' using a simple
-        top-down approach. The result has the form (<operator>, <list
-        containing parsed operands>).
-
-        feed -- _Feed instance containing the tokens for the expression.
-
-        cur_sym_or_choice -- The symbol or choice currently being parsed, or
-                             None if we're not parsing a symbol or choice.
-                             Used for recording references to symbols.
-
-        line -- The line containing the expression being parsed.
-
-        filename (default: None) -- The file containing the expression.
-
-        linenr (default: None) -- The line number containing the expression.
-
-        transform_m (default: False) -- Determines if 'm' should be rewritten to
-                                        'm && MODULES' -- see
-                                        parse_val_and_cond()."""
-
-        # Use instance variables to avoid having to pass these as arguments
-        # through the top-down parser in _parse_expr_2(), which is tedious and
-        # obfuscates the code. A profiler run shows no noticeable performance
-        # difference.
-        self.parse_expr_cur_sym_or_choice = cur_sym_or_choice
-        self.parse_expr_line = line
-        self.parse_expr_filename = filename
-        self.parse_expr_linenr = linenr
-        self.parse_expr_transform_m = transform_m
-
-        return self._parse_expr_2(feed)
-
-    def _parse_expr_2(self, feed):
-        or_terms = [self._parse_or_term(feed)]
-        # Keep parsing additional terms while the lookahead is '||'
-        while feed.check(T_OR):
-            or_terms.append(self._parse_or_term(feed))
-
-        return or_terms[0] if len(or_terms) == 1 else (OR, or_terms)
-
-    def _parse_or_term(self, feed):
-        and_terms = [self._parse_factor(feed)]
-        # Keep parsing additional terms while the lookahead is '&&'
-        while feed.check(T_AND):
-            and_terms.append(self._parse_factor(feed))
 
-        return and_terms[0] if len(and_terms) == 1 else (AND, and_terms)
-
-    def _parse_factor(self, feed):
-        if feed.check(T_OPEN_PAREN):
-            expr_parse = self._parse_expr_2(feed)
-
-            if not feed.check(T_CLOSE_PAREN):
-                _parse_error(self.parse_expr_line,
-                             "missing end parenthesis.",
-                             self.parse_expr_filename,
-                             self.parse_expr_linenr)
-
-            return expr_parse
-
-        if feed.check(T_NOT):
-            return (NOT, self._parse_factor(feed))
-
-        sym_or_string = feed.get_next()
-
-        if not isinstance(sym_or_string, (Symbol, str)):
-            _parse_error(self.parse_expr_line,
-                         "malformed expression.",
-                         self.parse_expr_filename,
-                         self.parse_expr_linenr)
-
-        if self.parse_expr_cur_sym_or_choice is not None and \
-           isinstance(sym_or_string, Symbol):
-            self.parse_expr_cur_sym_or_choice.referenced_syms.add(sym_or_string)
-
-        next_token = feed.peek_next()
-
-        # For conditional expressions ('depends on <expr>', '... if <expr>',
-        # etc.), "m" and m are rewritten to "m" && MODULES.
-        if next_token != T_EQUAL and next_token != T_UNEQUAL:
-            if self.parse_expr_transform_m and (sym_or_string is self.m or
-                                                sym_or_string == "m"):
-                return (AND, ["m", self._sym_lookup("MODULES")])
-            return sym_or_string
-
-        relation = EQUAL if (feed.get_next() == T_EQUAL) else UNEQUAL
-        sym_or_string_2 = feed.get_next()
-
-        if self.parse_expr_cur_sym_or_choice is not None and \
-           isinstance(sym_or_string_2, Symbol):
-            self.parse_expr_cur_sym_or_choice.referenced_syms.add(sym_or_string_2)
-
-        if sym_or_string is self.m:
-            sym_or_string = "m"
-
-        if sym_or_string_2 is self.m:
-            sym_or_string_2 = "m"
-
-        return (relation, sym_or_string, sym_or_string_2)
-
-    def _parse_file(self, filename, parent, deps, visible_if_deps, res = None):
-        """Parse the Kconfig file 'filename'. The result is a _Block with all
-        items from the file. See _parse_block() for the meaning of the
-        parameters."""
-        line_feeder = _FileFeed(_get_lines(filename), filename)
-        return self._parse_block(line_feeder, None, parent, deps, visible_if_deps, res)
+    def _parse_file(self, filename, parent, deps, visible_if_deps, res=None):
+        """Parses the Kconfig file 'filename'. Returns a list with the Items in
+        the file. See _parse_block() for the meaning of the parameters."""
+        return self._parse_block(_FileFeed(filename), None, parent, deps,
+                                 visible_if_deps, res)
 
     def _parse_block(self, line_feeder, end_marker, parent, deps,
-                     visible_if_deps = None, res = None):
+                     visible_if_deps, res=None):
         """Parses a block, which is the contents of either a file or an if,
-        menu, or choice statement. The result is a _Block with the items from
-        the block.
+        menu, or choice statement. Returns a list with the Items in the block.
 
-        end_marker -- The token that ends the block, e.g. T_ENDIF ("endif") for
-                      if's. None for files.
+        line_feeder: A _FileFeed instance feeding lines from a file. The
+          Kconfig language is line-based in practice.
 
-        parent -- The enclosing menu, choice or if, or None if we're at the top
-                  level.
+        end_marker: The token that ends the block, e.g. T_ENDIF ("endif") for
+           ifs. None for files.
 
-        deps -- Dependencies from enclosing menus, choices and if's.
+        parent: The enclosing menu or choice, or None if we're at the top
+           level.
 
-        visible_if_deps (default: None) -- 'visible if' dependencies from
-                        enclosing menus.
+        deps: Dependencies from enclosing menus, choices and ifs.
 
-        res (default: None) -- The _Block to add items to. If None, a new
-                               _Block is created to hold the items."""
+        visible_if_deps (default: None): 'visible if' dependencies from
+           enclosing menus.
 
-        block = _Block() if res is None else res
+        res (default: None): The list to add items to. If None, a new list is
+           created to hold the items."""
 
-        filename = line_feeder.get_filename()
+        block = [] if res is None else res
 
         while 1:
-
             # Do we already have a tokenized line that we determined wasn't
             # part of whatever we were parsing earlier? See comment in
             # Config.__init__().
             if self.end_line is not None:
-                assert self.end_line_tokens is not None
-                tokens = self.end_line_tokens
-                tokens.go_to_start()
-
                 line = self.end_line
-                linenr = line_feeder.get_linenr()
+                tokens = self.end_line_tokens
+                tokens.unget_all()
 
                 self.end_line = None
                 self.end_line_tokens = None
-
             else:
                 line = line_feeder.get_next()
                 if line is None:
                     if end_marker is not None:
-                        raise Kconfig_Syntax_Error, (
-                                "Unexpected end of file {0}."
-                                .format(line_feeder.get_filename()))
+                        raise Kconfig_Syntax_Error("Unexpected end of file {0}"
+                                                 .format(line_feeder.filename))
                     return block
 
-                linenr = line_feeder.get_linenr()
-
-                tokens = self._tokenize(line, False, filename, linenr)
-
-            if tokens.is_empty():
-                continue
+                tokens = self._tokenize(line, False, line_feeder.filename,
+                                        line_feeder.linenr)
 
             t0 = tokens.get_next()
+            if t0 is None:
+                continue
 
-            # Have we reached the end of the block?
-            if t0 == end_marker:
-                return block
+            # Cases are ordered roughly by frequency, which speeds things up a
+            # bit
 
             if t0 == T_CONFIG or t0 == T_MENUCONFIG:
                 # The tokenizer will automatically allocate a new Symbol object
@@ -1001,162 +670,154 @@ class Config():
                 sym = tokens.get_next()
 
                 # Symbols defined in multiple places get the parent of their
-                # first definition. However, for symbols whose parents are choice
-                # statements, the choice statement takes precedence.
+                # first definition. However, for symbols whose parents are
+                # choice statements, the choice statement takes precedence.
                 if not sym.is_defined_ or isinstance(parent, Choice):
                     sym.parent = parent
 
                 sym.is_defined_ = True
 
                 self.kconfig_syms.append(sym)
-                block.add_item(sym)
+                block.append(sym)
 
                 self._parse_properties(line_feeder, sym, deps, visible_if_deps)
 
+            elif t0 == T_SOURCE:
+                kconfig_file = tokens.get_next()
+                exp_kconfig_file = self._expand_sym_refs(kconfig_file)
+                f = os.path.join(self.base_dir, exp_kconfig_file)
+                if not os.path.exists(f):
+                    raise IOError('{0}:{1}: sourced file "{2}" (expands to '
+                                  '"{3}") not found. Perhaps base_dir '
+                                  '(argument to Config.__init__(), currently '
+                                  '"{4}") is set to the wrong value.'
+                                  .format(line_feeder.filename,
+                                          line_feeder.linenr,
+                                          kconfig_file, exp_kconfig_file,
+                                          self.base_dir))
+                # Add items to the same block
+                self._parse_file(f, parent, deps, visible_if_deps, block)
+
+            elif t0 == end_marker:
+                # We have reached the end of the block
+                return block
+
+            elif t0 == T_IF:
+                # If statements are treated as syntactic sugar for adding
+                # dependencies to enclosed items and do not have an explicit
+                # object representation.
+
+                dep_expr = self._parse_expr(tokens, None, line,
+                                            line_feeder.filename,
+                                            line_feeder.linenr)
+                # Add items to the same block
+                self._parse_block(line_feeder, T_ENDIF, parent,
+                                  _make_and(dep_expr, deps),
+                                  visible_if_deps, block)
+
+            elif t0 == T_COMMENT:
+                comment = Comment()
+
+                comment.config = self
+                comment.parent = parent
+                comment.filename = line_feeder.filename
+                comment.linenr = line_feeder.linenr
+                comment.text = tokens.get_next()
+
+                self.comments.append(comment)
+                block.append(comment)
+
+                self._parse_properties(line_feeder, comment, deps,
+                                       visible_if_deps)
+
             elif t0 == T_MENU:
                 menu = Menu()
-                self.menus.append(menu)
+
                 menu.config = self
                 menu.parent = parent
+                menu.filename = line_feeder.filename
+                menu.linenr = line_feeder.linenr
                 menu.title = tokens.get_next()
 
-                menu.filename = filename
-                menu.linenr = linenr
+                self.menus.append(menu)
+                block.append(menu)
 
                 # Parse properties and contents
-                self._parse_properties(line_feeder, menu, deps, visible_if_deps)
-                menu.block = self._parse_block(line_feeder,
-                                               T_ENDMENU,
-                                               menu,
+                self._parse_properties(line_feeder, menu, deps,
+                                       visible_if_deps)
+                menu.block = self._parse_block(line_feeder, T_ENDMENU, menu,
                                                menu.dep_expr,
                                                _make_and(visible_if_deps,
                                                          menu.visible_if_expr))
 
-                block.add_item(menu)
-
-            elif t0 == T_IF:
-                # If statements are treated as syntactic sugar for adding
-                # dependencies to enclosed items and do not have an explicit
-                # object representation.
-
-                dep_expr = self._parse_expr(tokens, None, line, filename, linenr)
-                self._parse_block(line_feeder,
-                                  T_ENDIF,
-                                  parent,
-                                  _make_and(dep_expr, deps),
-                                  visible_if_deps,
-                                  block) # Add items to the same block
-
             elif t0 == T_CHOICE:
-                # We support named choices
-                already_defined = False
-                name = None
-                if len(tokens) > 1 and isinstance(tokens[1], str):
-                    name = tokens[1]
-                    already_defined = name in self.named_choices
-
-                if already_defined:
-                    choice = self.named_choices[name]
-                else:
+                name = tokens.get_next()
+                if name is None:
                     choice = Choice()
                     self.choices.append(choice)
-                    if name is not None:
+                else:
+                    # Named choice
+                    choice = self.named_choices.get(name)
+                    if choice is None:
+                        choice = Choice()
                         choice.name = name
                         self.named_choices[name] = choice
+                        self.choices.append(choice)
 
                 choice.config = self
                 choice.parent = parent
 
-                choice.def_locations.append((filename, linenr))
+                choice.def_locations.append((line_feeder.filename,
+                                             line_feeder.linenr))
 
                 # Parse properties and contents
-                self._parse_properties(line_feeder, choice, deps, visible_if_deps)
-                choice.block = self._parse_block(line_feeder,
-                                                 T_ENDCHOICE,
-                                                 choice,
-                                                 deps,
-                                                 visible_if_deps)
+                self._parse_properties(line_feeder, choice, deps,
+                                       visible_if_deps)
+                choice.block = self._parse_block(line_feeder, T_ENDCHOICE,
+                                                 choice, deps, visible_if_deps)
 
                 choice._determine_actual_symbols()
 
-                # If no type is set for the choice, its type is that of the first
-                # choice item
+                # If no type is specified for the choice, its type is that of
+                # the first choice item with a specified type
                 if choice.type == UNKNOWN:
-                    for item in choice.get_symbols():
+                    for item in choice.actual_symbols:
                         if item.type != UNKNOWN:
                             choice.type = item.type
                             break
 
                 # Each choice item of UNKNOWN type gets the type of the choice
-                for item in choice.get_symbols():
+                for item in choice.actual_symbols:
                     if item.type == UNKNOWN:
                         item.type = choice.type
 
-                # For named choices defined in multiple locations, only record
-                # at the first definition
-                if not already_defined:
-                    block.add_item(choice)
-
-            elif t0 == T_COMMENT:
-                comment = Comment()
-                comment.config = self
-                comment.parent = parent
-
-                comment.filename = filename
-                comment.linenr = linenr
-
-                comment.text = tokens.get_next()
-                self._parse_properties(line_feeder, comment, deps, visible_if_deps)
-
-                block.add_item(comment)
-                self.comments.append(comment)
-
-            elif t0 == T_SOURCE:
-                kconfig_file = tokens.get_next()
-                exp_kconfig_file = self._expand_sym_refs(kconfig_file)
-                f = os.path.join(self.base_dir, exp_kconfig_file)
-
-                if not os.path.exists(f):
-                    raise IOError, ('{0}:{1}: sourced file "{2}" (expands to\n'
-                                    '"{3}") not found. Perhaps base_dir\n'
-                                    '(argument to Config.__init__(), currently\n'
-                                    '"{4}") is set to the wrong value.'
-                                    .format(filename,
-                                            linenr,
-                                            kconfig_file,
-                                            exp_kconfig_file,
-                                            self.base_dir))
-
-                # Add items to the same block
-                self._parse_file(f, parent, deps, visible_if_deps, block)
+                block.append(choice)
 
             elif t0 == T_MAINMENU:
                 text = tokens.get_next()
-
                 if self.mainmenu_text is not None:
                     self._warn("overriding 'mainmenu' text. "
                                'Old value: "{0}", new value: "{1}".'
-                                .format(self.mainmenu_text, text),
-                               filename,
-                               linenr)
-
+                               .format(self.mainmenu_text, text),
+                               line_feeder.filename, line_feeder.linenr)
                 self.mainmenu_text = text
 
             else:
-                _parse_error(line, "unrecognized construct.", filename, linenr)
+                _parse_error(line, "unrecognized construct",
+                             line_feeder.filename, line_feeder.linenr)
 
     def _parse_properties(self, line_feeder, stmt, deps, visible_if_deps):
-        """Parsing of properties for symbols, menus, choices, and comments."""
+        """Parsing of properties for symbols, menus, choices, and comments.
+        Takes care of propagating dependencies from enclosing menus and ifs."""
 
         def parse_val_and_cond(tokens, line, filename, linenr):
             """Parses '<expr1> if <expr2>' constructs, where the 'if' part is
             optional. Returns a tuple containing the parsed expressions, with
             None as the second element if the 'if' part is missing."""
             val = self._parse_expr(tokens, stmt, line, filename, linenr, False)
-
             if tokens.check(T_IF):
-                return (val, self._parse_expr(tokens, stmt, line, filename, linenr))
-
+                return (val, self._parse_expr(tokens, stmt, line, filename,
+                                              linenr))
             return (val, None)
 
         # In case the symbol is defined in multiple locations, we need to
@@ -1175,85 +836,61 @@ class Config():
             if line is None:
                 break
 
-            filename = line_feeder.get_filename()
-            linenr = line_feeder.get_linenr()
+            filename = line_feeder.filename
+            linenr = line_feeder.linenr
 
             tokens = self._tokenize(line, False, filename, linenr)
 
-            if tokens.is_empty():
+            t0 = tokens.get_next()
+            if t0 is None:
                 continue
 
-            t0 = tokens.get_next()
+            # Cases are ordered roughly by frequency, which speeds things up a
+            # bit
 
-            if t0 == T_HELP:
-                # Find first non-empty line and get its indentation
+            if t0 == T_DEPENDS:
+                if not tokens.check(T_ON):
+                    _parse_error(line, 'expected "on" after "depends"',
+                                 filename, linenr)
 
-                line_feeder.remove_while(str.isspace)
-                line = line_feeder.get_next()
+                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
+                                               linenr)
+
+                if isinstance(stmt, (Menu, Comment)):
+                    stmt.orig_deps = _make_and(stmt.orig_deps, parsed_deps)
+                else:
+                    depends_on_expr = _make_and(depends_on_expr, parsed_deps)
 
+            elif t0 == T_HELP:
+                # Find first non-blank (not all-space) line and get its
+                # indentation
+                line = line_feeder.next_nonblank()
                 if line is None:
                     stmt.help = ""
                     break
-
                 indent = _indentation(line)
-
-                # If the first non-empty lines has zero indent, there is no
-                # help text
                 if indent == 0:
+                    # If the first non-empty lines has zero indent, there is no
+                    # help text
                     stmt.help = ""
-                    line_feeder.go_back()
+                    line_feeder.unget()
                     break
 
-                help_lines = [_deindent(line, indent)]
-
                 # The help text goes on till the first non-empty line with less
                 # indent
+                help_lines = [_deindent(line, indent)]
                 while 1:
                     line = line_feeder.get_next()
-                    if (line is None) or \
+                    if line is None or \
                        (not line.isspace() and _indentation(line) < indent):
                         stmt.help = "".join(help_lines)
                         break
-
                     help_lines.append(_deindent(line, indent))
 
                 if line is None:
                     break
 
-                line_feeder.go_back()
-
-            elif t0 == T_PROMPT:
-                # 'prompt' properties override each other within a single
-                # definition of a symbol, but additional prompts can be added
-                # by defining the symbol multiple times; hence 'new_prompt'
-                # instead of 'prompt'.
-                new_prompt = parse_val_and_cond(tokens, line, filename, linenr)
-
-            elif t0 == T_DEFAULT:
-                new_def_exprs.append(parse_val_and_cond(tokens, line, filename, linenr))
-
-            elif t0 == T_DEPENDS:
-                if not tokens.check(T_ON):
-                    _parse_error(line, 'expected "on" after "depends".', filename, linenr)
-
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename, linenr)
-
-                if isinstance(stmt, (Menu, Comment)):
-                    stmt.dep_expr = _make_and(stmt.dep_expr, parsed_deps)
-                else:
-                    depends_on_expr = _make_and(depends_on_expr, parsed_deps)
-
-            elif t0 == T_VISIBLE:
-                if not tokens.check(T_IF):
-                    _parse_error(line, 'expected "if" after "visible".', filename, linenr)
-                if not isinstance(stmt, Menu):
-                    _parse_error(line,
-                                 "'visible if' is only valid for menus.",
-                                 filename,
-                                 linenr)
-
-                parsed_deps = self._parse_expr(tokens, stmt, line, filename, linenr)
-                stmt.visible_if_expr = _make_and(stmt.visible_if_expr, parsed_deps)
+                line_feeder.unget()
 
             elif t0 == T_SELECT:
                 target = tokens.get_next()
@@ -1263,47 +900,52 @@ class Config():
 
                 if tokens.check(T_IF):
                     new_selects.append((target,
-                                        self._parse_expr(tokens, stmt, line, filename, linenr)))
+                                        self._parse_expr(tokens, stmt, line,
+                                                         filename, linenr)))
                 else:
                     new_selects.append((target, None))
 
             elif t0 in (T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING):
-                stmt.type = token_to_type[t0]
+                stmt.type = TOKEN_TO_TYPE[t0]
+                if tokens.peek_next() is not None:
+                    new_prompt = parse_val_and_cond(tokens, line, filename,
+                                                    linenr)
+
+            elif t0 == T_DEFAULT:
+                new_def_exprs.append(parse_val_and_cond(tokens, line, filename,
+                                                        linenr))
+
+            elif t0 == T_DEF_BOOL:
+                stmt.type = BOOL
+                if tokens.peek_next() is not None:
+                    new_def_exprs.append(parse_val_and_cond(tokens, line,
+                                                            filename, linenr))
 
-                if len(tokens) > 1:
-                    new_prompt = parse_val_and_cond(tokens, line, filename, linenr)
+            elif t0 == T_PROMPT:
+                # 'prompt' properties override each other within a single
+                # definition of a symbol, but additional prompts can be added
+                # by defining the symbol multiple times; hence 'new_prompt'
+                # instead of 'prompt'.
+                new_prompt = parse_val_and_cond(tokens, line, filename, linenr)
 
             elif t0 == T_RANGE:
-                lower = tokens.get_next()
-                upper = tokens.get_next()
-                stmt.referenced_syms.add(lower)
-                stmt.referenced_syms.add(upper)
+                low = tokens.get_next()
+                high = tokens.get_next()
+                stmt.referenced_syms.add(low)
+                stmt.referenced_syms.add(high)
 
                 if tokens.check(T_IF):
-                    stmt.ranges.append((lower, upper,
-                                        self._parse_expr(tokens, stmt, line, filename, linenr)))
+                    stmt.ranges.append((low, high,
+                                        self._parse_expr(tokens, stmt, line,
+                                                         filename, linenr)))
                 else:
-                    stmt.ranges.append((lower, upper, None))
-
-            elif t0 == T_DEF_BOOL:
-                stmt.type = BOOL
-
-                if len(tokens) > 1:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line, filename, linenr))
+                    stmt.ranges.append((low, high, None))
 
             elif t0 == T_DEF_TRISTATE:
                 stmt.type = TRISTATE
-
-                if len(tokens) > 1:
-                    new_def_exprs.append(parse_val_and_cond(tokens, line, filename, linenr))
-
-            elif t0 == T_OPTIONAL:
-                if not isinstance(stmt, Choice):
-                    _parse_error(line,
-                                 '"optional" is only valid for choices.',
-                                 filename,
-                                 linenr)
-                stmt.optional = True
+                if tokens.peek_next() is not None:
+                    new_def_exprs.append(parse_val_and_cond(tokens, line,
+                                                            filename, linenr))
 
             elif t0 == T_OPTION:
                 if tokens.check(T_ENV) and tokens.check(T_EQUAL):
@@ -1313,44 +955,74 @@ class Config():
                     stmt.is_from_env = True
 
                     if env_var not in os.environ:
-                        self._warn("""
-The symbol {0} references the non-existent environment variable {1} and will
-get the empty string as its value.
-
-If you're using kconfiglib via 'make (i)scriptconfig' it should have set up the
-environment correctly for you. If you still got this message, that might be an
-error, and you should e-mail kconfiglib at gmail.com.
-."""                               .format(stmt.name, env_var),
-                                   filename,
-                                   linenr)
-
-                        stmt.cached_value = ""
+                        self._warn("The symbol {0} references the "
+                                   "non-existent environment variable {1} and "
+                                   "will get the empty string as its value. "
+                                   "If you're using Kconfiglib via "
+                                   "'make (i)scriptconfig', it should have "
+                                   "set up the environment correctly for you. "
+                                   "If you still got this message, that "
+                                   "might be an error, and you should email "
+                                   "ulfalizer a.t Google's email service."""
+                                   .format(stmt.name, env_var),
+                                   filename, linenr)
+
+                        stmt.cached_val = ""
                     else:
-                        stmt.cached_value = os.environ[env_var]
+                        stmt.cached_val = os.environ[env_var]
 
                 elif tokens.check(T_DEFCONFIG_LIST):
                     self.defconfig_sym = stmt
 
                 elif tokens.check(T_MODULES):
-                    self._warn("the 'modules' option is not supported. "
-                               "Let me know if this is a problem for you; "
-                               "it shouldn't be that hard to implement. "
-                               "(Note that modules are still supported -- "
-                               "Kconfiglib just assumes the symbol name "
-                               "MODULES.)",
-                               filename,
-                               linenr)
+                    # To reduce warning spam, only warn if 'option modules' is
+                    # set on some symbol that isn't MODULES, which should be
+                    # safe. I haven't run into any projects that make use
+                    # modules besides the kernel yet, and there it's likely to
+                    # keep being called "MODULES".
+                    if stmt.name != "MODULES":
+                        self._warn("the 'modules' option is not supported. "
+                                   "Let me know if this is a problem for you; "
+                                   "it shouldn't be that hard to implement. "
+                                   "(Note that modules are still supported -- "
+                                   "Kconfiglib just assumes the symbol name "
+                                   "MODULES, like older versions of the C "
+                                   "implementation did when 'option modules' "
+                                   "wasn't used.)",
+                                   filename, linenr)
 
                 elif tokens.check(T_ALLNOCONFIG_Y):
                     if not isinstance(stmt, Symbol):
                         _parse_error(line,
-                                     "the 'allnoconfig_y' option is only valid for symbols.",
-                                     filename,
-                                     linenr)
+                                     "the 'allnoconfig_y' option is only "
+                                     "valid for symbols",
+                                     filename, linenr)
                     stmt.allnoconfig_y = True
 
                 else:
-                    _parse_error(line, "unrecognized option.", filename, linenr)
+                    _parse_error(line, "unrecognized option", filename, linenr)
+
+            elif t0 == T_VISIBLE:
+                if not tokens.check(T_IF):
+                    _parse_error(line, 'expected "if" after "visible"',
+                                 filename, linenr)
+                if not isinstance(stmt, Menu):
+                    _parse_error(line,
+                                 "'visible if' is only valid for menus",
+                                 filename, linenr)
+
+                parsed_deps = self._parse_expr(tokens, stmt, line, filename,
+                                               linenr)
+                stmt.visible_if_expr = _make_and(stmt.visible_if_expr,
+                                                 parsed_deps)
+
+            elif t0 == T_OPTIONAL:
+                if not isinstance(stmt, Choice):
+                    _parse_error(line,
+                                 '"optional" is only valid for choices',
+                                 filename,
+                                 linenr)
+                stmt.optional = True
 
             else:
                 # See comment in Config.__init__()
@@ -1358,123 +1030,367 @@ error, and you should e-mail kconfiglib at gmail.com.
                 self.end_line_tokens = tokens
                 break
 
-        # Propagate dependencies from enclosing menus and if's.
+        # Done parsing properties. Now propagate 'depends on' and enclosing
+        # menu/if dependencies to expressions.
 
-        # For menus and comments..
-        if isinstance(stmt, (Menu, Comment)):
-            stmt.orig_deps = stmt.dep_expr
-            stmt.deps_from_containing = deps
-            stmt.dep_expr = _make_and(stmt.dep_expr, deps)
+        # The set of symbols referenced directly by the statement plus all
+        # symbols referenced by enclosing menus and ifs
+        stmt.all_referenced_syms = stmt.referenced_syms | _get_expr_syms(deps)
 
-            stmt.all_referenced_syms = \
-              stmt.referenced_syms | _get_expr_syms(deps)
+        # Save original dependencies from enclosing menus and ifs
+        stmt.deps_from_containing = deps
 
-        # For symbols and choices..
+        if isinstance(stmt, (Menu, Comment)):
+            stmt.dep_expr = _make_and(stmt.orig_deps, deps)
         else:
+            # Symbol or Choice
 
             # See comment for 'menu_dep'
             stmt.menu_dep = depends_on_expr
 
-            # Propagate dependencies specified with 'depends on' to any new
-            # default expressions, prompts, and selections. ("New" since a
-            # symbol might be defined in multiple places and the dependencies
-            # should only apply to the local definition.)
-
-            new_def_exprs = [(val_expr, _make_and(cond_expr, depends_on_expr))
-                             for (val_expr, cond_expr) in new_def_exprs]
-
-            new_selects = [(target, _make_and(cond_expr, depends_on_expr))
-                           for (target, cond_expr) in new_selects]
+            # Propagate dependencies to prompts
 
             if new_prompt is not None:
+                # Propagate 'visible if' dependencies from enclosing menus
                 prompt, cond_expr = new_prompt
-
-                # 'visible if' dependencies from enclosing menus get propagated
-                # to prompts
-                if visible_if_deps is not None:
-                    cond_expr = _make_and(cond_expr, visible_if_deps)
-
+                cond_expr = _make_and(cond_expr, visible_if_deps)
+                # Propagate 'depends on' dependencies
                 new_prompt = (prompt, _make_and(cond_expr, depends_on_expr))
+                # Save original
+                stmt.orig_prompts.append(new_prompt)
+                # Finalize with dependencies from enclosing menus and ifs
+                stmt.prompts.append((new_prompt[0],
+                                     _make_and(new_prompt[1], deps)))
 
-            # We save the original expressions -- before any menu and if
-            # conditions have been propagated -- so these can be retrieved
-            # later.
+            # Propagate dependencies to defaults
 
+            # Propagate 'depends on' dependencies
+            new_def_exprs = [(val_expr, _make_and(cond_expr, depends_on_expr))
+                             for val_expr, cond_expr in new_def_exprs]
+            # Save original
             stmt.orig_def_exprs.extend(new_def_exprs)
-            if new_prompt is not None:
-                stmt.orig_prompts.append(new_prompt)
+            # Finalize with dependencies from enclosing menus and ifs
+            stmt.def_exprs.extend([(val_expr, _make_and(cond_expr, deps))
+                                   for val_expr, cond_expr in new_def_exprs])
+
+            # Propagate dependencies to selects
 
             # Only symbols can select
             if isinstance(stmt, Symbol):
+                # Propagate 'depends on' dependencies
+                new_selects = [(target, _make_and(cond_expr, depends_on_expr))
+                               for target, cond_expr in new_selects]
+                # Save original
                 stmt.orig_selects.extend(new_selects)
+                # Finalize with dependencies from enclosing menus and ifs
+                for target, cond in new_selects:
+                    target.rev_dep = _make_or(target.rev_dep,
+                                              _make_and(stmt,
+                                                        _make_and(cond, deps)))
 
-            # Save dependencies from enclosing menus and if's
-            stmt.deps_from_containing = deps
+    def _parse_expr(self, feed, cur_item, line, filename=None, linenr=None,
+                    transform_m=True):
+        """Parses an expression from the tokens in 'feed' using a simple
+        top-down approach. The result has the form
+        '(<operator>, [<parsed operands>])', where <operator> is e.g.
+        kconfiglib.AND. If there is only one operand (i.e., no && or ||), then
+        the operand is returned directly. This also goes for subexpressions.
 
-            # The set of symbols referenced directly by the symbol/choice plus
-            # all symbols referenced by enclosing menus and if's.
-            stmt.all_referenced_syms = \
-              stmt.referenced_syms | _get_expr_syms(deps)
+        feed: _Feed instance containing the tokens for the expression.
 
-            # Propagate dependencies from enclosing menus and if's
+        cur_item: The item (Symbol, Choice, Menu, or Comment) currently being
+           parsed, or None if we're not parsing an item. Used for recording
+           references to symbols.
 
-            stmt.def_exprs.extend([(val_expr, _make_and(cond_expr, deps))
-                                   for (val_expr, cond_expr) in new_def_exprs])
+        line: The line containing the expression being parsed.
 
-            for (target, cond) in new_selects:
-                target.rev_dep = _make_or(target.rev_dep,
-                                          _make_and(stmt,
-                                                    _make_and(cond, deps)))
+        filename (default: None): The file containing the expression.
 
-            if new_prompt is not None:
-                prompt, cond_expr = new_prompt
-                stmt.prompts.append((prompt, _make_and(cond_expr, deps)))
+        linenr (default: None): The line number containing the expression.
 
-    #
-    # Symbol table manipulation
-    #
+        transform_m (default: False): Determines if 'm' should be rewritten to
+           'm && MODULES' -- see parse_val_and_cond().
+
+        Expression grammar, in decreasing order of precedence:
+
+        <expr> -> <symbol>
+                  <symbol> '=' <symbol>
+                  <symbol> '!=' <symbol>
+                  '(' <expr> ')'
+                  '!' <expr>
+                  <expr> '&&' <expr>
+                  <expr> '||' <expr>"""
+
+        # Use instance variables to avoid having to pass these as arguments
+        # through the top-down parser in _parse_expr_rec(), which is tedious
+        # and obfuscates the code. A profiler run shows no noticeable
+        # performance difference.
+        self._cur_item = cur_item
+        self._transform_m = transform_m
+        self._line = line
+        self._filename = filename
+        self._linenr = linenr
+
+        return self._parse_expr_rec(feed)
+
+    def _parse_expr_rec(self, feed):
+        or_term = self._parse_or_term(feed)
+        if not feed.check(T_OR):
+            # Common case -- no need for an OR node since it's just a single
+            # operand
+            return or_term
+        or_terms = [or_term, self._parse_or_term(feed)]
+        while feed.check(T_OR):
+            or_terms.append(self._parse_or_term(feed))
+        return (OR, or_terms)
+
+    def _parse_or_term(self, feed):
+        and_term = self._parse_factor(feed)
+        if not feed.check(T_AND):
+            # Common case -- no need for an AND node since it's just a single
+            # operand
+            return and_term
+        and_terms = [and_term, self._parse_factor(feed)]
+        while feed.check(T_AND):
+            and_terms.append(self._parse_factor(feed))
+        return (AND, and_terms)
+
+    def _parse_factor(self, feed):
+        token = feed.get_next()
+
+        if isinstance(token, (Symbol, str)):
+            if self._cur_item is not None and isinstance(token, Symbol):
+                self._cur_item.referenced_syms.add(token)
+
+            next_token = feed.peek_next()
+            # For conditional expressions ('depends on <expr>',
+            # '... if <expr>', # etc.), "m" and m are rewritten to
+            # "m" && MODULES.
+            if next_token != T_EQUAL and next_token != T_UNEQUAL:
+                if self._transform_m and (token is self.m or token == "m"):
+                    return (AND, ["m", self._sym_lookup("MODULES")])
+                return token
+
+            relation = EQUAL if (feed.get_next() == T_EQUAL) else UNEQUAL
+            token_2 = feed.get_next()
+            if self._cur_item is not None and isinstance(token_2, Symbol):
+                self._cur_item.referenced_syms.add(token_2)
+            return (relation, token, token_2)
+
+        if token == T_NOT:
+            return (NOT, self._parse_factor(feed))
+
+        if token == T_OPEN_PAREN:
+            expr_parse = self._parse_expr_rec(feed)
+            if not feed.check(T_CLOSE_PAREN):
+                _parse_error(self._line, "missing end parenthesis",
+                             self._filename, self._linenr)
+            return expr_parse
+
+        _parse_error(self._line, "malformed expression", self._filename,
+                     self._linenr)
+
+    def _tokenize(self, s, for_eval, filename=None, linenr=None):
+        """Returns a _Feed instance containing tokens derived from the string
+        's'. Registers any new symbols encountered (via _sym_lookup()).
+
+        (I experimented with a pure regular expression implementation, but it
+        came out slower, less readable, and wouldn't have been as flexible.)
+
+        for_eval: True when parsing an expression for a call to Config.eval(),
+           in which case we should not treat the first token specially nor
+           register new symbols."""
+
+        s = s.strip()
+        if s == "" or s[0] == "#":
+            return _Feed([])
+
+        if for_eval:
+            previous = None # The previous token seen
+            tokens = []
+            i = 0 # The current index in the string being tokenized
+
+        else:
+            # The initial word on a line is parsed specially. Let
+            # command_chars = [A-Za-z0-9_]. Then
+            #  - leading non-command_chars characters are ignored, and
+            #  - the first token consists the following one or more
+            #    command_chars characters.
+            # This is why things like "----help--" are accepted.
+            initial_token_match = _initial_token_re_match(s)
+            if initial_token_match is None:
+                return _Feed([])
+            keyword = _get_keyword(initial_token_match.group(1))
+            if keyword == T_HELP:
+                # Avoid junk after "help", e.g. "---", being registered as a
+                # symbol
+                return _Feed([T_HELP])
+            if keyword is None:
+                # We expect a keyword as the first token
+                _tokenization_error(s, filename, linenr)
+
+            previous = keyword
+            tokens = [keyword]
+            # The current index in the string being tokenized
+            i = initial_token_match.end()
+
+        # _tokenize() is a hotspot during parsing, and this speeds things up a
+        # bit
+        strlen = len(s)
+        append = tokens.append
+
+        # Main tokenization loop. (Handles tokens past the first one.)
+        while i < strlen:
+            # Test for an identifier/keyword preceded by whitespace first; this
+            # is the most common case.
+            id_keyword_match = _id_keyword_re_match(s, i)
+            if id_keyword_match:
+                # We have an identifier or keyword. The above also stripped any
+                # whitespace for us.
+                name = id_keyword_match.group(1)
+                # Jump past it
+                i = id_keyword_match.end()
+
+                keyword = _get_keyword(name)
+                if keyword is not None:
+                    # It's a keyword
+                    append(keyword)
+                elif previous in STRING_LEX:
+                    # What would ordinarily be considered an identifier is
+                    # treated as a string after certain tokens
+                    append(name)
+                else:
+                    # It's a symbol name. _sym_lookup() will take care of
+                    # allocating a new Symbol instance if it's the first time
+                    # we see it.
+                    sym = self._sym_lookup(name, for_eval)
+
+                    if previous == T_CONFIG or previous == T_MENUCONFIG:
+                        # If the previous token is T_(MENU)CONFIG
+                        # ("(menu)config"), we're tokenizing the first line of
+                        # a symbol definition, and should remember this as a
+                        # location where the symbol is defined
+                        sym.def_locations.append((filename, linenr))
+                    else:
+                        # Otherwise, it's a reference to the symbol
+                        sym.ref_locations.append((filename, linenr))
+
+                    append(sym)
+
+            else:
+                # Not an identifier/keyword
+
+                while i < strlen and s[i].isspace():
+                    i += 1
+                if i == strlen:
+                    break
+                c = s[i]
+                i += 1
+
+                # String literal (constant symbol)
+                if c == '"' or c == "'":
+                    if "\\" in s:
+                        # Slow path: This could probably be sped up, but it's a
+                        # very unusual case anyway.
+                        quote = c
+                        val = ""
+                        while 1:
+                            if i >= len(s):
+                                _tokenization_error(s, filename, linenr)
+                            c = s[i]
+                            if c == quote:
+                                break
+                            if c == "\\":
+                                if i + 1 >= len(s):
+                                    _tokenization_error(s, filename, linenr)
+                                val += s[i + 1]
+                                i += 2
+                            else:
+                                val += c
+                                i += 1
+                        i += 1
+                        append(val)
+                    else:
+                        # Fast path: If the string contains no backslashes
+                        # (almost always) we can simply look for the matching
+                        # quote.
+                        end = s.find(c, i)
+                        if end == -1:
+                            _tokenization_error(s, filename, linenr)
+                        append(s[i:end])
+                        i = end + 1
+
+                elif c == "&":
+                    # Invalid characters are ignored
+                    if i >= len(s) or s[i] != "&": continue
+                    append(T_AND)
+                    i += 1
+
+                elif c == "|":
+                    # Invalid characters are ignored
+                    if i >= len(s) or s[i] != "|": continue
+                    append(T_OR)
+                    i += 1
+
+                elif c == "!":
+                    if i < len(s) and s[i] == "=":
+                        append(T_UNEQUAL)
+                        i += 1
+                    else:
+                        append(T_NOT)
+
+                elif c == "=": append(T_EQUAL)
+                elif c == "(": append(T_OPEN_PAREN)
+                elif c == ")": append(T_CLOSE_PAREN)
+                elif c == "#": break # Comment
 
-    def _sym_lookup(self, name, add_sym_if_not_exists = True):
-        """Fetches the symbol 'name' from the symbol table, optionally adding
-        it if it does not exist (this is usually what we want)."""
+                else: continue # Invalid characters are ignored
+
+            previous = tokens[-1]
+
+        return _Feed(tokens)
+
+    def _sym_lookup(self, name, for_eval=False):
+        """Fetches the symbol 'name' from the symbol table, creating and
+        registering it if it does not exist. If 'for_eval' is True, the symbol
+        won't be added to the symbol table if it does not exist -- this is for
+        Config.eval()."""
         if name in self.syms:
             return self.syms[name]
 
         new_sym = Symbol()
         new_sym.config = self
         new_sym.name = name
-
-        if add_sym_if_not_exists:
-            self.syms[name] = new_sym
-        else:
-            # This warning is generated while evaluating an expression
-            # containing undefined symbols using Config.eval()
+        if for_eval:
             self._warn("no symbol {0} in configuration".format(name))
-
+        else:
+            self.syms[name] = new_sym
         return new_sym
 
     #
-    # Evaluation of symbols and expressions
+    # Expression evaluation
     #
 
     def _eval_expr(self, expr):
-        """Evaluates an expression and returns one of the tristate values "n",
-        "m" or "y"."""
-        res = self._eval_expr_2(expr)
-
-        # Promote "m" to "y" if we're running without modules. Internally, "m"
-        # is often rewritten to "m" && MODULES by both the C implementation and
-        # kconfiglib, which takes care of cases where "m" should be false if
-        # we're running without modules.
-        if res == "m" and not self._has_modules():
-            return "y"
-
-        return res
+        """Evaluates an expression to "n", "m", or "y"."""
 
-    def _eval_expr_2(self, expr):
+        # Handles e.g. an "x if y" condition where the "if y" part is missing.
         if expr is None:
             return "y"
 
+        res = self._eval_expr_rec(expr)
+        if res == "m":
+            # Promote "m" to "y" if we're running without modules.
+            #
+            # Internally, "m" is often rewritten to "m" && MODULES by both the
+            # C implementation and Kconfiglib, which takes care of cases where
+            # "m" should be demoted to "n" instead.
+            modules_sym = self.syms.get("MODULES")
+            if modules_sym is None or modules_sym.get_value() != "y":
+                return "y"
+        return res
+
+    def _eval_expr_rec(self, expr):
         if isinstance(expr, Symbol):
             # Non-bool/tristate symbols are always "n" in a tristate sense,
             # regardless of their value
@@ -1485,89 +1401,65 @@ error, and you should e-mail kconfiglib at gmail.com.
         if isinstance(expr, str):
             return expr if (expr == "y" or expr == "m") else "n"
 
-        first_expr = expr[0]
-
-        if first_expr == OR:
-            res = "n"
-
-            for subexpr in expr[1]:
-                ev = self._eval_expr_2(subexpr)
-
-                # Return immediately upon discovering a "y" term
-                if ev == "y":
-                    return "y"
-
-                if ev == "m":
-                    res = "m"
-
-            # 'res' is either "n" or "m" here; we already handled the
-            # short-circuiting "y" case in the loop.
-            return res
+        # Ordered by frequency
 
-        if first_expr == AND:
+        if expr[0] == AND:
             res = "y"
-
             for subexpr in expr[1]:
-                ev = self._eval_expr_2(subexpr)
-
+                ev = self._eval_expr_rec(subexpr)
                 # Return immediately upon discovering an "n" term
                 if ev == "n":
                     return "n"
-
                 if ev == "m":
                     res = "m"
-
             # 'res' is either "m" or "y" here; we already handled the
             # short-circuiting "n" case in the loop.
             return res
 
-        if first_expr == NOT:
-            ev = self._eval_expr_2(expr[1])
-
+        if expr[0] == NOT:
+            ev = self._eval_expr_rec(expr[1])
             if ev == "y":
                 return "n"
-
             return "y" if (ev == "n") else "m"
 
-        if first_expr == EQUAL:
-            return "y" if (self._get_str_value(expr[1]) ==
-                           self._get_str_value(expr[2])) else "n"
-
-        if first_expr == UNEQUAL:
-            return "y" if (self._get_str_value(expr[1]) !=
-                           self._get_str_value(expr[2])) else "n"
-
-        _internal_error("Internal error while evaluating expression: "
-                        "unknown operation {0}.".format(first_expr))
+        if expr[0] == OR:
+            res = "n"
+            for subexpr in expr[1]:
+                ev = self._eval_expr_rec(subexpr)
+                # Return immediately upon discovering a "y" term
+                if ev == "y":
+                    return "y"
+                if ev == "m":
+                    res = "m"
+            # 'res' is either "n" or "m" here; we already handled the
+            # short-circuiting "y" case in the loop.
+            return res
 
-    def _get_str_value(self, obj):
-        if isinstance(obj, str):
-            return obj
-        # obj is a Symbol
-        return obj.get_value()
+        if expr[0] == EQUAL:
+            return "y" if (_str_val(expr[1]) == _str_val(expr[2])) else "n"
+
+        if expr[0] == UNEQUAL:
+            return "y" if (_str_val(expr[1]) != _str_val(expr[2])) else "n"
+
+        _internal_error("Internal error while evaluating expression: "
+                        "unknown operation {0}.".format(expr[0]))
 
     def _eval_min(self, e1, e2):
+        """Returns the minimum value of the two expressions. Equates None with
+        'y'."""
         e1_eval = self._eval_expr(e1)
         e2_eval = self._eval_expr(e2)
-
         return e1_eval if tri_less(e1_eval, e2_eval) else e2_eval
 
     def _eval_max(self, e1, e2):
+        """Returns the maximum value of the two expressions. Equates None with
+        'y'."""
         e1_eval = self._eval_expr(e1)
         e2_eval = self._eval_expr(e2)
-
         return e1_eval if tri_greater(e1_eval, e2_eval) else e2_eval
 
     #
-    # Methods related to the MODULES symbol
-    #
-
-    def _has_modules(self):
-        modules_sym = self.syms.get("MODULES")
-        return (modules_sym is not None) and (modules_sym.get_value() == "y")
-
-    #
-    # Dependency tracking
+    # Dependency tracking (for caching and invalidation)
     #
 
     def _build_dep(self):
@@ -1577,8 +1469,6 @@ error, and you should e-mail kconfiglib at gmail.com.
         for caching/invalidation purposes. The calculated sets might be larger
         than necessary as we don't do any complicated analysis of the
         expressions."""
-        for sym in self.syms.itervalues():
-            sym.dep = set()
 
         # Adds 'sym' as a directly dependent symbol to all symbols that appear
         # in the expression 'e'
@@ -1593,62 +1483,121 @@ error, and you should e-mail kconfiglib at gmail.com.
         #    (these won't be included in 'dep' as that makes the dependency
         #    graph unwieldy, but Symbol._get_dependent() will include them)
         #  - Any symbols in a choice statement that depends on the symbol
-        for sym in self.syms.itervalues():
-            for (_, e) in sym.prompts:
+        for sym in self.syms_iter():
+            for _, e in sym.prompts:
                 add_expr_deps(e, sym)
 
-            for (v, e) in sym.def_exprs:
+            for v, e in sym.def_exprs:
                 add_expr_deps(v, sym)
                 add_expr_deps(e, sym)
 
             add_expr_deps(sym.rev_dep, sym)
 
-            for (l, u, e) in sym.ranges:
+            for l, u, e in sym.ranges:
                 add_expr_deps(l, sym)
                 add_expr_deps(u, sym)
                 add_expr_deps(e, sym)
 
-            if sym.is_choice_symbol_:
+            if sym.is_choice_sym:
                 choice = sym.parent
-
-                for (_, e) in choice.prompts:
+                for _, e in choice.prompts:
                     add_expr_deps(e, sym)
-
-                for (_, e) in choice.def_exprs:
+                for _, e in choice.def_exprs:
                     add_expr_deps(e, sym)
 
-    def _expr_val_str(self, expr, no_value_str = "(none)", get_val_instead_of_eval = False):
-        # Since values are valid expressions, _expr_to_str() will get a nice
-        # string representation for those as well.
+    def _eq_to_sym(self, eq):
+        """_expr_depends_on() helper. For (in)equalities of the form sym = y/m
+        or sym != n, returns sym. For other (in)equalities, returns None."""
+        relation, left, right = eq
+
+        def transform_y_m_n(item):
+            if item is self.y: return "y"
+            if item is self.m: return "m"
+            if item is self.n: return "n"
+            return item
+
+        left = transform_y_m_n(left)
+        right = transform_y_m_n(right)
+
+        # Make sure the symbol (if any) appears to the left
+        if not isinstance(left, Symbol):
+            left, right = right, left
+        if not isinstance(left, Symbol):
+            return None
+        if (relation == EQUAL and (right == "y" or right == "m")) or \
+           (relation == UNEQUAL and right == "n"):
+            return left
+        return None
 
+    def _expr_depends_on(self, expr, sym):
+        """Reimplementation of expr_depends_symbol() from mconf.c. Used to
+        determine if a submenu should be implicitly created, which influences
+        what items inside choice statements are considered choice items."""
         if expr is None:
-            return no_value_str
+            return False
 
-        if get_val_instead_of_eval:
+        def rec(expr):
             if isinstance(expr, str):
-                return _expr_to_str(expr)
-            val = expr.get_value()
-        else:
-            val = self._eval_expr(expr)
+                return False
+            if isinstance(expr, Symbol):
+                return expr is sym
 
-        return "{0} (value: {1})".format(_expr_to_str(expr), _expr_to_str(val))
+            if expr[0] in (EQUAL, UNEQUAL):
+                return self._eq_to_sym(expr) is sym
+            if expr[0] == AND:
+                for and_expr in expr[1]:
+                    if rec(and_expr):
+                        return True
+            return False
+
+        return rec(expr)
+
+    def _invalidate_all(self):
+        for sym in self.syms_iter():
+            sym._invalidate()
+
+    #
+    # Printing and misc.
+    #
 
     def _expand_sym_refs(self, s):
         """Expands $-references to symbols in 's' to symbol values, or to the
         empty string for undefined symbols."""
 
         while 1:
-            sym_ref_re_match = sym_ref_re.search(s)
-            if sym_ref_re_match is None:
+            sym_ref_match = _sym_ref_re_search(s)
+            if sym_ref_match is None:
                 return s
 
-            sym_name = sym_ref_re_match.group(0)[1:]
+            sym_name = sym_ref_match.group(0)[1:]
             sym = self.syms.get(sym_name)
             expansion = "" if sym is None else sym.get_value()
 
-            s = s[:sym_ref_re_match.start()] + \
+            s = s[:sym_ref_match.start()] + \
                 expansion + \
-                s[sym_ref_re_match.end():]
+                s[sym_ref_match.end():]
+
+    def _expr_val_str(self, expr, no_value_str="(none)",
+                      get_val_instead_of_eval=False):
+        """Printing helper. Returns a string with 'expr' and its value.
+
+        no_value_str: String to return when 'expr' is missing (None).
+
+        get_val_instead_of_eval: Assume 'expr' is a symbol or string (constant
+          symbol) and get its value directly instead of evaluating it to a
+          tristate value."""
+
+        if expr is None:
+            return no_value_str
+
+        if get_val_instead_of_eval:
+            if isinstance(expr, str):
+                return _expr_to_str(expr)
+            val = expr.get_value()
+        else:
+            val = self._eval_expr(expr)
+
+        return "{0} (value: {1})".format(_expr_to_str(expr), _expr_to_str(val))
 
     def _get_sym_or_choice_str(self, sc):
         """Symbols and choices have many properties in common, so we factor out
@@ -1662,679 +1611,300 @@ error, and you should e-mail kconfiglib at gmail.com.
         # Common symbol/choice properties
         #
 
-        user_value_str = "(no user value)" if sc.user_val is None else s(sc.user_val)
-
-        visibility_str = s(sc.get_visibility())
+        user_val_str = "(no user value)" if sc.user_val is None else \
+                       s(sc.user_val)
 
         # Build prompts string
-        if sc.prompts == []:
+        if not sc.prompts:
             prompts_str = " (no prompts)"
         else:
             prompts_str_rows = []
-
-            for (prompt, cond_expr) in sc.orig_prompts:
+            for prompt, cond_expr in sc.orig_prompts:
                 if cond_expr is None:
                     prompts_str_rows.append(' "{0}"'.format(prompt))
                 else:
-                    prompts_str_rows.append(' "{0}" if '.format(prompt) +
-                                            self._expr_val_str(cond_expr))
-
+                    prompts_str_rows.append(
+                      ' "{0}" if {1}'.format(prompt,
+                                             self._expr_val_str(cond_expr)))
             prompts_str = "\n".join(prompts_str_rows)
 
         # Build locations string
-        if sc.def_locations == []:
+        if not sc.def_locations:
             locations_str = "(no locations)"
         else:
             locations_str = " ".join(["{0}:{1}".format(filename, linenr) for
                                       (filename, linenr) in sc.def_locations])
 
-        # Build additional-dependencies-from-menus-and-if's string
-        additional_deps_str = " " + self._expr_val_str(sc.deps_from_containing,
-                                                       "(no additional dependencies)")
+        # Build additional-dependencies-from-menus-and-ifs string
+        additional_deps_str = " " + \
+          self._expr_val_str(sc.deps_from_containing,
+                             "(no additional dependencies)")
 
         #
         # Symbol-specific stuff
         #
 
         if isinstance(sc, Symbol):
-
-            # Build value string
-            value_str = s(sc.get_value())
-
             # Build ranges string
             if isinstance(sc, Symbol):
-                if sc.ranges == []:
+                if not sc.ranges:
                     ranges_str = " (no ranges)"
                 else:
                     ranges_str_rows = []
-
-                    for (l, u, cond_expr) in sc.ranges:
+                    for l, u, cond_expr in sc.ranges:
                         if cond_expr is None:
-                            ranges_str_rows.append(" [{0}, {1}]".format(s(l), s(u)))
+                            ranges_str_rows.append(" [{0}, {1}]".format(s(l),
+                                                                        s(u)))
                         else:
                             ranges_str_rows.append(" [{0}, {1}] if {2}"
-                                                   .format(s(l), s(u), self._expr_val_str(cond_expr)))
-
+                              .format(s(l), s(u),
+                                      self._expr_val_str(cond_expr)))
                     ranges_str = "\n".join(ranges_str_rows)
 
             # Build default values string
-            if sc.def_exprs == []:
+            if not sc.def_exprs:
                 defaults_str = " (no default values)"
             else:
                 defaults_str_rows = []
-
-                for (val_expr, cond_expr) in sc.orig_def_exprs:
-                    row_str = " " + self._expr_val_str(val_expr, "(none)", sc.type == STRING)
+                for val_expr, cond_expr in sc.orig_def_exprs:
+                    row_str = " " + self._expr_val_str(val_expr, "(none)",
+                                                       sc.type == STRING)
                     defaults_str_rows.append(row_str)
-                    defaults_str_rows.append("  Condition: " + self._expr_val_str(cond_expr))
-
+                    defaults_str_rows.append("  Condition: " +
+                                               self._expr_val_str(cond_expr))
                 defaults_str = "\n".join(defaults_str_rows)
 
             # Build selects string
-            if sc.orig_selects == []:
+            if not sc.orig_selects:
                 selects_str = " (no selects)"
-            else:
-                selects_str_rows = []
-
-                for (target, cond_expr) in sc.orig_selects:
-                    if cond_expr is None:
-                        selects_str_rows.append(" {0}".format(target.name))
-                    else:
-                        selects_str_rows.append(" {0} if ".format(target.name) +
-                                                self._expr_val_str(cond_expr))
-
-                selects_str = "\n".join(selects_str_rows)
-
-            # Build reverse dependencies string
-            if sc.rev_dep == "n":
-                rev_dep_str = " (no reverse dependencies)"
-            else:
-                rev_dep_str = " " + self._expr_val_str(sc.rev_dep)
-
-            res = _sep_lines("Symbol " + (sc.name if sc.name is not None else "(no name)"),
-                             "Type           : " + typename[sc.type],
-                             "Value          : " + value_str,
-                             "User value     : " + user_value_str,
-                             "Visibility     : " + visibility_str,
-                             "Is choice item : " + bool_str[sc.is_choice_symbol_],
-                             "Is defined     : " + bool_str[sc.is_defined_],
-                             "Is from env.   : " + bool_str[sc.is_from_env],
-                             "Is special     : " + bool_str[sc.is_special_] + "\n")
-
-            if sc.ranges != []:
-                res += _sep_lines("Ranges:",
-                                  ranges_str + "\n")
-
-            res += _sep_lines("Prompts:",
-                              prompts_str,
-                              "Default values:",
-                              defaults_str,
-                              "Selects:",
-                              selects_str,
-                              "Reverse dependencies:",
-                              rev_dep_str,
-                              "Additional dependencies from enclosing menus and if's:",
-                              additional_deps_str,
-                              "Locations: " + locations_str)
-
-            return res
-
-        #
-        # Choice-specific stuff
-        #
-
-        # Build name string (for named choices)
-        if sc.name is None:
-            name_str = "(no name)"
-        else:
-            name_str = sc.name
-
-        # Build selected symbol string
-        sel = sc.get_selection()
-        if sel is None:
-            sel_str = "(no selection)"
-        else:
-            sel_str = sel.name
-
-        # Build mode string
-        mode_str = s(sc.get_mode())
-
-        # Build default values string
-        if sc.def_exprs == []:
-            defaults_str = " (no default values)"
-        else:
-            defaults_str_rows = []
-
-            for (sym, cond_expr) in sc.orig_def_exprs:
-                if cond_expr is None:
-                    defaults_str_rows.append(" {0}".format(sym.name))
-                else:
-                    defaults_str_rows.append(" {0} if ".format(sym.name) +
-                                             self._expr_val_str(cond_expr))
-
-            defaults_str = "\n".join(defaults_str_rows)
-
-        # Build contained symbols string
-        names = [sym.name for sym in sc.get_symbols()]
-
-        if names == []:
-            syms_string = "(empty)"
-        else:
-            syms_string = " ".join(names)
-
-        return _sep_lines("Choice",
-                          "Name (for named choices): " + name_str,
-                          "Type            : " + typename[sc.type],
-                          "Selected symbol : " + sel_str,
-                          "User value      : " + user_value_str,
-                          "Mode            : " + mode_str,
-                          "Visibility      : " + visibility_str,
-                          "Optional        : " + bool_str[sc.optional],
-                          "Prompts:",
-                          prompts_str,
-                          "Defaults:",
-                          defaults_str,
-                          "Choice symbols:",
-                          " " + syms_string,
-                          "Additional dependencies from enclosing menus and if's:",
-                          additional_deps_str,
-                          "Locations: " + locations_str)
-
-    def _expr_depends_on(self, expr, sym):
-        """Reimplementation of expr_depends_symbol() from mconf.c. Used to
-        determine if a submenu should be implicitly created, which influences what
-        items inside choice statements are considered choice items."""
-        if expr is None:
-            return False
-
-        def rec(expr):
-            if isinstance(expr, str):
-                return False
-
-            if isinstance(expr, Symbol):
-                return expr is sym
-
-            e0 = expr[0]
-
-            if e0 == EQUAL or e0 == UNEQUAL:
-                return self._eq_to_sym(expr) is sym
-
-            if e0 == AND:
-                for and_expr in expr[1]:
-                    if rec(and_expr):
-                        return True
-
-            return False
-
-        return rec(expr)
-
-    def _eq_to_sym(self, eq):
-        """_expr_depends_on() helper. For (in)equalities of the form sym = y/m
-        or sym != n, returns sym. For other (in)equalities, returns None."""
-        relation, left, right = eq
-
-        left  = self._transform_n_m_y(left)
-        right = self._transform_n_m_y(right)
-
-        # Make sure the symbol (if any) appears to the left
-        if not isinstance(left, Symbol):
-            left, right = right, left
-
-        if not isinstance(left, Symbol):
-            return None
-
-        if (relation == EQUAL   and (right == "m" or right == "y")) or \
-           (relation == UNEQUAL and right == "n"):
-            return left
-
-        return None
-
-    def _transform_n_m_y(self, item):
-        """_eq_to_sym() helper. Translates the symbols n, m, and y to their
-        string equivalents."""
-        if item is self.n:
-            return "n"
-        if item is self.m:
-            return "m"
-        if item is self.y:
-            return "y"
-        return item
-
-    def _warn(self, msg, filename = None, linenr = None):
-        """For printing warnings to stderr."""
-        if self.print_warnings:
-            self._warn_or_undef_assign(msg, WARNING, filename, linenr)
-
-    def _undef_assign(self, msg, filename = None, linenr = None):
-        """For printing informational messages related to assignments
-        to undefined variables to stderr."""
-        if self.print_undef_assign:
-            self._warn_or_undef_assign(msg, UNDEF_ASSIGN, filename, linenr)
-
-    def _warn_or_undef_assign(self, msg, msg_type, filename, linenr):
-        if filename is not None:
-            sys.stderr.write("{0}:".format(_clean_up_path(filename)))
-        if linenr is not None:
-            sys.stderr.write("{0}:".format(linenr))
-
-        if msg_type == WARNING:
-            sys.stderr.write("warning: ")
-        elif msg_type == UNDEF_ASSIGN:
-            sys.stderr.write("info: ")
-        else:
-            _internal_error('Internal error while printing warning: unknown warning type "{0}".'
-                            .format(msg_type))
-
-        sys.stderr.write(msg + "\n")
-
-def _get_expr_syms(expr):
-    """Returns the set() of symbols appearing in expr."""
-    res = set()
-    if expr is None:
-        return res
-
-    def rec(expr):
-        if isinstance(expr, Symbol):
-            res.add(expr)
-            return
-
-        if isinstance(expr, str):
-            return
-
-        e0 = expr[0]
-
-        if e0 == OR or e0 == AND:
-            for term in expr[1]:
-                rec(term)
-
-        elif e0 == NOT:
-            rec(expr[1])
-
-        elif e0 == EQUAL or e0 == UNEQUAL:
-            _, v1, v2 = expr
-
-            if isinstance(v1, Symbol):
-                res.add(v1)
-
-            if isinstance(v2, Symbol):
-                res.add(v2)
-
-        else:
-            _internal_error("Internal error while fetching symbols from an "
-                            "expression with token stream {0}.".format(expr))
-
-    rec(expr)
-    return res
-
-
-#
-# Construction of expressions
-#
-
-# These functions as well as the _eval_min/max() functions above equate
-# None with "y", which is usually what we want, but needs to be kept in
-# mind.
-
-def _make_or(e1, e2):
-    # Perform trivial simplification and avoid None's (which
-    # correspond to y's)
-    if e1 is None or e2 is None or \
-       e1 == "y" or e2 == "y":
-        return "y"
-
-    if e1 == "n":
-        return e2
-
-    if e2 == "n":
-        return e1
-
-    # Prefer to merge/update argument list if possible instead of creating
-    # a new OR node
-
-    if isinstance(e1, tuple) and e1[0] == OR:
-        if isinstance(e2, tuple) and e2[0] == OR:
-            return (OR, e1[1] + e2[1])
-        return (OR, e1[1] + [e2])
-
-    if isinstance(e2, tuple) and e2[0] == OR:
-        return (OR, e2[1] + [e1])
-
-    return (OR, [e1, e2])
-
-# Note: returns None if e1 == e2 == None
-
-def _make_and(e1, e2):
-    if e1 == "n" or e2 == "n":
-        return "n"
-
-    if e1 is None or e1 == "y":
-        return e2
-
-    if e2 is None or e2 == "y":
-        return e1
-
-    # Prefer to merge/update argument list if possible instead of creating
-    # a new AND node
-
-    if isinstance(e1, tuple) and e1[0] == AND:
-        if isinstance(e2, tuple) and e2[0] == AND:
-            return (AND, e1[1] + e2[1])
-        return (AND, e1[1] + [e2])
-
-    if isinstance(e2, tuple) and e2[0] == AND:
-        return (AND, e2[1] + [e1])
-
-    return (AND, [e1, e2])
-
-#
-# Constants and functions related to types, parsing, evaluation and printing,
-# put globally to unclutter the Config class a bit.
-#
-
-# Tokens
-(T_OR, T_AND, T_NOT,
- T_OPEN_PAREN, T_CLOSE_PAREN,
- T_EQUAL, T_UNEQUAL,
- T_MAINMENU, T_MENU, T_ENDMENU,
- T_SOURCE, T_CHOICE, T_ENDCHOICE,
- T_COMMENT, T_CONFIG, T_MENUCONFIG,
- T_HELP, T_IF, T_ENDIF, T_DEPENDS, T_ON,
- T_OPTIONAL, T_PROMPT, T_DEFAULT,
- T_BOOL, T_TRISTATE, T_HEX, T_INT, T_STRING,
- T_DEF_BOOL, T_DEF_TRISTATE,
- T_SELECT, T_RANGE, T_OPTION, T_ALLNOCONFIG_Y, T_ENV,
- T_DEFCONFIG_LIST, T_MODULES, T_VISIBLE) = range(0, 39)
-
-# Keyword to token map
-keywords = {
-        "mainmenu"       : T_MAINMENU,
-        "menu"           : T_MENU,
-        "endmenu"        : T_ENDMENU,
-        "endif"          : T_ENDIF,
-        "endchoice"      : T_ENDCHOICE,
-        "source"         : T_SOURCE,
-        "choice"         : T_CHOICE,
-        "config"         : T_CONFIG,
-        "comment"        : T_COMMENT,
-        "menuconfig"     : T_MENUCONFIG,
-        "help"           : T_HELP,
-        "if"             : T_IF,
-        "depends"        : T_DEPENDS,
-        "on"             : T_ON,
-        "optional"       : T_OPTIONAL,
-        "prompt"         : T_PROMPT,
-        "default"        : T_DEFAULT,
-        "bool"           : T_BOOL,
-        "boolean"        : T_BOOL,
-        "tristate"       : T_TRISTATE,
-        "int"            : T_INT,
-        "hex"            : T_HEX,
-        "def_bool"       : T_DEF_BOOL,
-        "def_tristate"   : T_DEF_TRISTATE,
-        "string"         : T_STRING,
-        "select"         : T_SELECT,
-        "range"          : T_RANGE,
-        "option"         : T_OPTION,
-        "allnoconfig_y"  : T_ALLNOCONFIG_Y,
-        "env"            : T_ENV,
-        "defconfig_list" : T_DEFCONFIG_LIST,
-        "modules"        : T_MODULES,
-        "visible"        : T_VISIBLE }
-
-# Strings to use for True and False
-bool_str = { False : "false", True : "true" }
-
-# Tokens after which identifier-like lexemes are treated as strings. T_CHOICE
-# is included to avoid symbols being registered for named choices.
-string_lex = frozenset((T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING, T_CHOICE,
-                        T_PROMPT, T_MENU, T_COMMENT, T_SOURCE, T_MAINMENU))
-
-# Matches the initial token on a line; see _tokenize().
-initial_token_re = re.compile(r"[^\w]*(\w+)")
-
-# Matches an identifier/keyword optionally preceded by whitespace
-id_keyword_re = re.compile(r"\s*([\w./-]+)")
-
-# Regular expressions for parsing .config files
-set_re   = re.compile(r"CONFIG_(\w+)=(.*)")
-unset_re = re.compile(r"# CONFIG_(\w+) is not set")
-
-# Regular expression for finding $-references to symbols in strings
-sym_ref_re = re.compile(r"\$[A-Za-z0-9_]+")
-
-# Integers representing symbol types
-UNKNOWN, BOOL, TRISTATE, STRING, HEX, INT = range(0, 6)
-
-# Strings to use for types
-typename = {
-        UNKNOWN  : "unknown",
-        BOOL     : "bool",
-        TRISTATE : "tristate",
-        STRING   : "string",
-        HEX      : "hex",
-        INT      : "int" }
-
-# Token to type mapping
-token_to_type = { T_BOOL     : BOOL,
-                  T_TRISTATE : TRISTATE,
-                  T_STRING   : STRING,
-                  T_INT      : INT,
-                  T_HEX      : HEX }
-
-# Default values for symbols of different types (the value the symbol gets if
-# it is not assigned a user value and none of its 'default' clauses kick in)
-default_value = { BOOL     : "n",
-                  TRISTATE : "n",
-                  STRING   : "",
-                  INT      : "",
-                  HEX      : "" }
-
-# Indicates that no item is selected in a choice statement
-NO_SELECTION = 0
-
-# Integers representing expression types
-OR, AND, NOT, EQUAL, UNEQUAL = range(0, 5)
-
-# Map from tristate values to integers
-tri_to_int = { "n" : 0, "m" : 1, "y" : 2 }
-
-# Printing-related stuff
-
-op_to_str = { AND     : " && ",
-              OR      : " || ",
-              EQUAL   : " = ",
-              UNEQUAL : " != " }
-
-precedence = { OR : 0, AND : 1, NOT : 2 }
-
-# Types of informational messages
-WARNING = 0
-UNDEF_ASSIGN = 1
-
-def _intersperse(lst, op):
-    """_expr_to_str() helper. Gets the string representation of each expression in lst
-    and produces a list where op has been inserted between the elements."""
-    if lst == []:
-        return ""
-
-    res = []
-
-    def handle_sub_expr(expr):
-        no_parens = isinstance(expr, (str, Symbol)) or \
-                    expr[0] in (EQUAL, UNEQUAL) or \
-                    precedence[op] <= precedence[expr[0]]
-        if not no_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr))
-        if not no_parens:
-            res.append(")")
-
-    op_str = op_to_str[op]
-
-    handle_sub_expr(lst[0])
-    for expr in lst[1:]:
-        res.append(op_str)
-        handle_sub_expr(expr)
-
-    return res
-
-def _expr_to_str(expr):
-    s = "".join(_expr_to_str_rec(expr))
-    return s
-
-def _sym_str_string(sym_or_str):
-    if isinstance(sym_or_str, str):
-        return '"{0}"'.format(sym_or_str)
-    return sym_or_str.name
-
-def _expr_to_str_rec(expr):
-    if expr is None:
-        return [""]
-
-    if isinstance(expr, (Symbol, str)):
-        return [_sym_str_string(expr)]
-
-    e0 = expr[0]
-
-    if e0 == OR or e0 == AND:
-        return _intersperse(expr[1], expr[0])
-
-    if e0 == NOT:
-        need_parens = not isinstance(expr[1], (str, Symbol))
-
-        res = ["!"]
-        if need_parens:
-            res.append("(")
-        res.extend(_expr_to_str_rec(expr[1]))
-        if need_parens:
-            res.append(")")
-        return res
-
-    if e0 == EQUAL or e0 == UNEQUAL:
-        return [_sym_str_string(expr[1]),
-                op_to_str[expr[0]],
-                _sym_str_string(expr[2])]
-
-class _Block:
-
-    """Represents a list of items (symbols, menus, choice statements and
-    comments) appearing at the top-level of a file or witin a menu, choice or
-    if statement."""
+            else:
+                selects_str_rows = []
+                for target, cond_expr in sc.orig_selects:
+                    if cond_expr is None:
+                        selects_str_rows.append(" {0}".format(target.name))
+                    else:
+                        selects_str_rows.append(
+                          " {0} if {1}".format(target.name,
+                                               self._expr_val_str(cond_expr)))
+                selects_str = "\n".join(selects_str_rows)
 
-    def __init__(self):
-        self.items = []
+            res = _lines("Symbol " +
+                           ("(no name)" if sc.name is None else sc.name),
+                         "Type           : " + TYPENAME[sc.type],
+                         "Value          : " + s(sc.get_value()),
+                         "User value     : " + user_val_str,
+                         "Visibility     : " + s(_get_visibility(sc)),
+                         "Is choice item : " + BOOL_STR[sc.is_choice_sym],
+                         "Is defined     : " + BOOL_STR[sc.is_defined_],
+                         "Is from env.   : " + BOOL_STR[sc.is_from_env],
+                         "Is special     : " + BOOL_STR[sc.is_special_] + "\n")
+            if sc.ranges:
+                res += _lines("Ranges:", ranges_str + "\n")
+            res += _lines("Prompts:",
+                          prompts_str,
+                          "Default values:",
+                          defaults_str,
+                          "Selects:",
+                          selects_str,
+                          "Reverse (select-related) dependencies:",
+                          " (no reverse dependencies)" if sc.rev_dep == "n"
+                            else " " + self._expr_val_str(sc.rev_dep),
+                          "Additional dependencies from enclosing menus "
+                            "and ifs:",
+                          additional_deps_str,
+                          "Locations: " + locations_str)
 
-    def get_items(self):
-        return self.items
+            return res
 
-    def add_item(self, item):
-        self.items.append(item)
+        #
+        # Choice-specific stuff
+        #
 
-    def _make_conf(self):
-        # Collect the substrings in a list and later use join() instead of +=
-        # to build the final .config contents. With older Python versions, this
-        # yields linear instead of quadratic complexity.
-        strings = []
-        for item in self.items:
-            strings.extend(item._make_conf())
+        # Build selected symbol string
+        sel = sc.get_selection()
+        sel_str = "(no selection)" if sel is None else sel.name
 
-        return strings
+        # Build default values string
+        if not sc.def_exprs:
+            defaults_str = " (no default values)"
+        else:
+            defaults_str_rows = []
+            for sym, cond_expr in sc.orig_def_exprs:
+                if cond_expr is None:
+                    defaults_str_rows.append(" {0}".format(sym.name))
+                else:
+                    defaults_str_rows.append(" {0} if {1}".format(sym.name,
+                                                self._expr_val_str(cond_expr)))
+            defaults_str = "\n".join(defaults_str_rows)
 
-    def add_depend_expr(self, expr):
-        for item in self.items:
-            item.add_depend_expr(expr)
+        # Build contained symbols string
+        names = [sym.name for sym in sc.actual_symbols]
+        syms_string = " ".join(names) if names else "(empty)"
+
+        return _lines("Choice",
+                      "Name (for named choices): " +
+                        ("(no name)" if sc.name is None else sc.name),
+                      "Type            : " + TYPENAME[sc.type],
+                      "Selected symbol : " + sel_str,
+                      "User value      : " + user_val_str,
+                      "Mode            : " + s(sc.get_mode()),
+                      "Visibility      : " + s(_get_visibility(sc)),
+                      "Optional        : " + BOOL_STR[sc.optional],
+                      "Prompts:",
+                      prompts_str,
+                      "Defaults:",
+                      defaults_str,
+                      "Choice symbols:",
+                      " " + syms_string,
+                      "Additional dependencies from enclosing menus and "
+                        "ifs:",
+                      additional_deps_str,
+                      "Locations: " + locations_str)
+
+    def _warn(self, msg, filename=None, linenr=None):
+        """For printing warnings to stderr."""
+        if self.print_warnings:
+            _stderr_msg("warning: " + msg, filename, linenr)
 
-class Item():
+class Item(object):
 
     """Base class for symbols and other Kconfig constructs. Subclasses are
     Symbol, Choice, Menu, and Comment."""
 
     def is_symbol(self):
-        """Returns True if the item is a symbol, otherwise False. Short for
+        """Returns True if the item is a symbol. Short for
         isinstance(item, kconfiglib.Symbol)."""
         return isinstance(self, Symbol)
 
     def is_choice(self):
-        """Returns True if the item is a choice, otherwise False. Short for
+        """Returns True if the item is a choice. Short for
         isinstance(item, kconfiglib.Choice)."""
         return isinstance(self, Choice)
 
     def is_menu(self):
-        """Returns True if the item is a menu, otherwise False. Short for
+        """Returns True if the item is a menu. Short for
         isinstance(item, kconfiglib.Menu)."""
         return isinstance(self, Menu)
 
     def is_comment(self):
-        """Returns True if the item is a comment, otherwise False. Short for
+        """Returns True if the item is a comment. Short for
         isinstance(item, kconfiglib.Comment)."""
         return isinstance(self, Comment)
 
-class _HasVisibility():
+class Symbol(Item):
 
-    """Base class for elements that have a "visibility" that acts as an upper
-    limit on the values a user can set for them. Subclasses are Symbol and
-    Choice (which supply some of the attributes)."""
+    """Represents a configuration symbol - e.g. FOO for
 
-    def __init__(self):
-        self.cached_visibility = None
-        self.prompts = []
+    config FOO
+        ..."""
 
-    def _invalidate(self):
-        self.cached_visibility = None
+    #
+    # Public interface
+    #
 
-    def _get_visibility(self):
-        if self.cached_visibility is None:
-            vis = "n"
-            for (prompt, cond_expr) in self.prompts:
-                vis = self.config._eval_max(vis, cond_expr)
+    def get_config(self):
+        """Returns the Config instance this symbol is from."""
+        return self.config
 
-            if isinstance(self, Symbol) and self.is_choice_symbol_:
-                vis = self.config._eval_min(vis, self.parent._get_visibility())
+    def get_name(self):
+        """Returns the name of the symbol."""
+        return self.name
 
-            # Promote "m" to "y" if we're dealing with a non-tristate
-            if vis == "m" and self.type != TRISTATE:
-                vis = "y"
+    def get_type(self):
+        """Returns the type of the symbol: one of UNKNOWN, BOOL, TRISTATE,
+        STRING, HEX, or INT. These are defined at the top level of the module,
+        so you'd do something like
 
-            self.cached_visibility = vis
+        if sym.get_type() == kconfiglib.STRING:
+            ..."""
+        return self.type
 
-        return self.cached_visibility
+    def get_prompts(self):
+        """Returns a list of prompts defined for the symbol, in the order they
+        appear in the configuration files. Returns the empty list for symbols
+        with no prompt.
 
-class Symbol(Item, _HasVisibility):
+        This list will have a single entry for the vast majority of symbols
+        having prompts, but having multiple prompts for a single symbol is
+        possible through having multiple 'config' entries for it."""
+        return [prompt for prompt, _ in self.orig_prompts]
 
-    """Represents a configuration symbol - e.g. FOO for
+    def get_help(self):
+        """Returns the help text of the symbol, or None if the symbol has no
+        help text."""
+        return self.help
 
-    config FOO
-        ..."""
+    def get_parent(self):
+        """Returns the menu or choice statement that contains the symbol, or
+        None if the symbol is at the top level. Note that if statements are
+        treated as syntactic and do not have an explicit class
+        representation."""
+        return self.parent
 
-    #
-    # Public interface
-    #
+    def get_def_locations(self):
+        """Returns a list of (filename, linenr) tuples, where filename (string)
+        and linenr (int) represent a location where the symbol is defined. For
+        the vast majority of symbols this list will only contain one element.
+        For the following Kconfig, FOO would get two entries: the lines marked
+        with *.
+
+        config FOO *
+            bool "foo prompt 1"
+
+        config FOO *
+            bool "foo prompt 2"
+        """
+        return self.def_locations
+
+    def get_ref_locations(self):
+        """Returns a list of (filename, linenr) tuples, where filename (string)
+        and linenr (int) represent a location where the symbol is referenced in
+        the configuration. For example, the lines marked by * would be included
+        for FOO below:
+
+        config A
+            bool
+            default BAR || FOO *
+
+        config B
+            tristate
+            depends on FOO *
+            default m if FOO *
+
+        if FOO *
+            config A
+                bool "A"
+        endif
+
+        config FOO (definition not included)
+            bool
+        """
+        return self.ref_locations
 
     def get_value(self):
         """Calculate and return the value of the symbol. See also
         Symbol.set_user_value()."""
 
-        if self.cached_value is not None:
-            return self.cached_value
-
-        self.write_to_conf = False
+        if self.cached_val is not None:
+            return self.cached_val
 
         # As a quirk of Kconfig, undefined symbols get their name as their
         # value. This is why things like "FOO = bar" work for seeing if FOO has
         # the value "bar".
         if self.type == UNKNOWN:
-            self.cached_value = self.name
+            self.cached_val = self.name
             return self.name
 
-        new_val = default_value[self.type]
+        new_val = DEFAULT_VALUE[self.type]
+        vis = _get_visibility(self)
 
-        vis = self._get_visibility()
+        # This is easiest to calculate together with the value
+        self.write_to_conf = False
 
         if self.type == BOOL or self.type == TRISTATE:
             # The visibility and mode (modules-only or single-selection) of
-            # choice items will be taken into account in self._get_visibility()
-
-            if self.is_choice_symbol_:
+            # choice items will be taken into account in _get_visibility()
+            if self.is_choice_sym:
                 if vis != "n":
                     choice = self.parent
                     mode = choice.get_mode()
@@ -2342,35 +1912,36 @@ class Symbol(Item, _HasVisibility):
                     self.write_to_conf = (mode != "n")
 
                     if mode == "y":
-                        new_val = "y" if (choice.get_selection() is self) else "n"
+                        if choice.get_selection() is self:
+                            new_val = "y"
+                        else:
+                            new_val = "n"
                     elif mode == "m":
                         if self.user_val == "m" or self.user_val == "y":
                             new_val = "m"
 
             else:
+                # If the symbol is visible and has a user value, use that.
+                # Otherwise, look at defaults.
                 use_defaults = True
 
                 if vis != "n":
-                    # If the symbol is visible and has a user value, use that.
-                    # Otherwise, look at defaults.
                     self.write_to_conf = True
-
                     if self.user_val is not None:
                         new_val = self.config._eval_min(self.user_val, vis)
                         use_defaults = False
 
                 if use_defaults:
-                    for (val_expr, cond_expr) in self.def_exprs:
+                    for val_expr, cond_expr in self.def_exprs:
                         cond_eval = self.config._eval_expr(cond_expr)
-
                         if cond_eval != "n":
                             self.write_to_conf = True
-                            new_val = self.config._eval_min(val_expr, cond_eval)
+                            new_val = self.config._eval_min(val_expr,
+                                                            cond_eval)
                             break
 
-                # Reverse dependencies take precedence
+                # Reverse (select-related) dependencies take precedence
                 rev_dep_val = self.config._eval_expr(self.rev_dep)
-
                 if rev_dep_val != "n":
                     self.write_to_conf = True
                     new_val = self.config._eval_max(new_val, rev_dep_val)
@@ -2379,23 +1950,7 @@ class Symbol(Item, _HasVisibility):
             if new_val == "m" and self.type == BOOL:
                 new_val = "y"
 
-        elif self.type == STRING:
-            use_defaults = True
-
-            if vis != "n":
-                self.write_to_conf = True
-                if self.user_val is not None:
-                    new_val = self.user_val
-                    use_defaults = False
-
-            if use_defaults:
-                for (val_expr, cond_expr) in self.def_exprs:
-                    if self.config._eval_expr(cond_expr) != "n":
-                        self.write_to_conf = True
-                        new_val = self.config._get_str_value(val_expr)
-                        break
-
-        elif self.type == HEX or self.type == INT:
+        elif self.type == INT or self.type == HEX:
             has_active_range = False
             low = None
             high = None
@@ -2403,13 +1958,12 @@ class Symbol(Item, _HasVisibility):
 
             base = 16 if self.type == HEX else 10
 
-            for(l, h, cond_expr) in self.ranges:
+            for l, h, cond_expr in self.ranges:
                 if self.config._eval_expr(cond_expr) != "n":
                     has_active_range = True
 
-                    low_str = self.config._get_str_value(l)
-                    high_str = self.config._get_str_value(h)
-
+                    low_str = _str_val(l)
+                    high_str = _str_val(h)
                     low = int(low_str, base) if \
                       _is_base_n(low_str, base) else 0
                     high = int(high_str, base) if \
@@ -2433,7 +1987,7 @@ class Symbol(Item, _HasVisibility):
                     new_val = self.user_val
 
             if use_defaults:
-                for (val_expr, cond_expr) in self.def_exprs:
+                for val_expr, cond_expr in self.def_exprs:
                     if self.config._eval_expr(cond_expr) != "n":
                         self.write_to_conf = True
 
@@ -2442,7 +1996,7 @@ class Symbol(Item, _HasVisibility):
                         # to the range, and the output has "0x" as appropriate
                         # for the type.
 
-                        new_val = self.config._get_str_value(val_expr)
+                        new_val = _str_val(val_expr)
 
                         if _is_base_n(new_val, base):
                             new_val_num = int(new_val, base)
@@ -2463,93 +2017,54 @@ class Symbol(Item, _HasVisibility):
                     # If no user value or default kicks in but the hex/int has
                     # an active range, then the low end of the range is used,
                     # provided it's > 0, with "0x" prepended as appropriate.
-
                     if has_active_range and low > 0:
                         new_val = (hex(low) if self.type == HEX else str(low))
 
-        self.cached_value = new_val
-        return new_val
-
-    def set_user_value(self, v):
-        """Sets the user value of the symbol.
-
-        Equal in effect to assigning the value to the symbol within a .config
-        file. Use get_lower/upper_bound() or get_assignable_values() to find
-        the range of currently assignable values for bool and tristate symbols;
-        setting values outside this range will cause the user value to differ
-        from the result of Symbol.get_value() (be truncated). Values that are
-        invalid for the type (such as a_bool.set_user_value("foo")) are
-        ignored, and a warning is emitted if an attempt is made to assign such
-        a value.
-
-        For any type of symbol, is_modifiable() can be used to check if a user
-        value will currently have any effect on the symbol, as determined by
-        its visibility and range of assignable values. Any value that is valid
-        for the type (bool, tristate, etc.) will end up being reflected in
-        get_user_value() though, and might have an effect later if conditions
-        change. To get rid of the user value, use unset_user_value().
-
-        Any symbols dependent on the symbol are (recursively) invalidated, so
-        things will just work with regards to dependencies.
-
-        v -- The user value to give to the symbol."""
-        self._set_user_value_no_invalidate(v, False)
+        elif self.type == STRING:
+            use_defaults = True
 
-        # There might be something more efficient you could do here, but play
-        # it safe.
-        if self.name == "MODULES":
-            self.config._invalidate_all()
-            return
+            if vis != "n":
+                self.write_to_conf = True
+                if self.user_val is not None:
+                    new_val = self.user_val
+                    use_defaults = False
 
-        self._invalidate()
-        self._invalidate_dependent()
+            if use_defaults:
+                for val_expr, cond_expr in self.def_exprs:
+                    if self.config._eval_expr(cond_expr) != "n":
+                        self.write_to_conf = True
+                        new_val = _str_val(val_expr)
+                        break
 
-    def unset_user_value(self):
-        """Resets the user value of the symbol, as if the symbol had never
-        gotten a user value via Config.load_config() or
-        Symbol.set_user_value()."""
-        self._unset_user_value_no_recursive_invalidate()
-        self._invalidate_dependent()
+        self.cached_val = new_val
+        return new_val
 
     def get_user_value(self):
         """Returns the value assigned to the symbol in a .config or via
-        Symbol.set_user_value() (provided the value was valid for the type of the
-        symbol). Returns None in case of no user value."""
+        Symbol.set_user_value() (provided the value was valid for the type of
+        the symbol). Returns None in case of no user value."""
         return self.user_val
 
-    def get_name(self):
-        """Returns the name of the symbol."""
-        return self.name
-
-    def get_prompts(self):
-        """Returns a list of prompts defined for the symbol, in the order they
-        appear in the configuration files. Returns the empty list for symbols
-        with no prompt.
-
-        This list will have a single entry for the vast majority of symbols
-        having prompts, but having multiple prompts for a single symbol is
-        possible through having multiple 'config' entries for it."""
-        return [prompt for prompt, _ in self.orig_prompts]
-
     def get_upper_bound(self):
         """For string/hex/int symbols and for bool and tristate symbols that
         cannot be modified (see is_modifiable()), returns None.
 
         Otherwise, returns the highest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "m" or "y",
-        arranged from lowest to highest. This corresponds to the highest value
-        the symbol could be given in e.g. the 'make menuconfig' interface.
+        Symbol.set_user_value() (that will not be truncated): one of "m" or
+        "y", arranged from lowest to highest. This corresponds to the highest
+        value the symbol could be given in e.g. the 'make menuconfig'
+        interface.
 
         See also the tri_less*() and tri_greater*() functions, which could come
         in handy."""
         if self.type != BOOL and self.type != TRISTATE:
             return None
         rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y"
-        if self.type == BOOL and rev_dep == "m":
-            rev_dep = "y"
-        vis = self._get_visibility()
-        if (tri_to_int[vis] - tri_to_int[rev_dep]) > 0:
+        # A bool selected to "m" gets promoted to "y", pinning it
+        if rev_dep == "m" and self.type == BOOL:
+            return None
+        vis = _get_visibility(self)
+        if TRI_TO_INT[vis] > TRI_TO_INT[rev_dep]:
             return vis
         return None
 
@@ -2558,19 +2073,20 @@ class Symbol(Item, _HasVisibility):
         cannot be modified (see is_modifiable()), returns None.
 
         Otherwise, returns the lowest value the symbol can be set to with
-        Symbol.set_user_value() (that will not be truncated): one of "n" or "m",
-        arranged from lowest to highest. This corresponds to the lowest value
-        the symbol could be given in e.g. the 'make menuconfig' interface.
+        Symbol.set_user_value() (that will not be truncated): one of "n" or
+        "m", arranged from lowest to highest. This corresponds to the lowest
+        value the symbol could be given in e.g. the 'make menuconfig'
+        interface.
 
         See also the tri_less*() and tri_greater*() functions, which could come
         in handy."""
         if self.type != BOOL and self.type != TRISTATE:
             return None
         rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y"
-        if self.type == BOOL and rev_dep == "m":
-            rev_dep = "y"
-        if (tri_to_int[self._get_visibility()] - tri_to_int[rev_dep]) > 0:
+        # A bool selected to "m" gets promoted to "y", pinning it
+        if rev_dep == "m" and self.type == BOOL:
+            return None
+        if TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]:
             return rev_dep
         return None
 
@@ -2590,22 +2106,13 @@ class Symbol(Item, _HasVisibility):
         if self.type != BOOL and self.type != TRISTATE:
             return []
         rev_dep = self.config._eval_expr(self.rev_dep)
-        # A bool selected to "m" gets promoted to "y"
-        if self.type == BOOL and rev_dep == "m":
-            rev_dep = "y"
-        res = ["n", "m", "y"][tri_to_int[rev_dep] :
-                              tri_to_int[self._get_visibility()] + 1]
+        # A bool selected to "m" gets promoted to "y", pinning it
+        if rev_dep == "m" and self.type == BOOL:
+            return []
+        res = ["n", "m", "y"][TRI_TO_INT[rev_dep] :
+                              TRI_TO_INT[_get_visibility(self)] + 1]
         return res if len(res) > 1 else []
 
-    def get_type(self):
-        """Returns the type of the symbol: one of UNKNOWN, BOOL, TRISTATE,
-        STRING, HEX, or INT. These are defined at the top level of the module,
-        so you'd do something like
-
-        if sym.get_type() == kconfiglib.STRING:
-            ..."""
-        return self.type
-
     def get_visibility(self):
         """Returns the visibility of the symbol: one of "n", "m" or "y". For
         bool and tristate symbols, this is an upper bound on the value users
@@ -2648,16 +2155,9 @@ class Symbol(Item, _HasVisibility):
 
         You should probably look at get_lower/upper_bound(),
         get_assignable_values() and is_modifiable() before using this."""
-        return self._get_visibility()
-
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the symbol, or
-        None if the symbol is at the top level. Note that if statements are
-        treated as syntactic and do not have an explicit class
-        representation."""
-        return self.parent
+        return _get_visibility(self)
 
-    def get_referenced_symbols(self, refs_from_enclosing = False):
+    def get_referenced_symbols(self, refs_from_enclosing=False):
         """Returns the set() of all symbols referenced by this symbol. For
         example, the symbol defined by
 
@@ -2670,10 +2170,10 @@ class Symbol(Item, _HasVisibility):
 
         references the symbols A through G.
 
-        refs_from_enclosing (default: False) -- If True, the symbols
-                            referenced by enclosing menus and if's will be
-                            included in the result."""
-        return self.all_referenced_syms if refs_from_enclosing else self.referenced_syms
+        refs_from_enclosing (default: False): If True, the symbols referenced
+           by enclosing menus and ifs will be included in the result."""
+        return self.all_referenced_syms if refs_from_enclosing else \
+               self.referenced_syms
 
     def get_selected_symbols(self):
         """Returns the set() of all symbols X for which this symbol has a
@@ -2682,58 +2182,50 @@ class Symbol(Item, _HasVisibility):
         get_referenced_symbols()."""
         return self.selected_syms
 
-    def get_help(self):
-        """Returns the help text of the symbol, or None if the symbol has no
-        help text."""
-        return self.help
-
-    def get_config(self):
-        """Returns the Config instance this symbol is from."""
-        return self.config
-
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is defined. For
-        the vast majority of symbols this list will only contain one element.
-        For the following Kconfig, FOO would get two entries: the lines marked
-        with *.
-
-        config FOO *
-            bool "foo prompt 1"
+    def set_user_value(self, v):
+        """Sets the user value of the symbol.
 
-        config FOO *
-            bool "foo prompt 2"
-        """
-        return self.def_locations
+        Equal in effect to assigning the value to the symbol within a .config
+        file. Use get_lower/upper_bound() or get_assignable_values() to find
+        the range of currently assignable values for bool and tristate symbols;
+        setting values outside this range will cause the user value to differ
+        from the result of Symbol.get_value() (be truncated). Values that are
+        invalid for the type (such as a_bool.set_user_value("foo")) are
+        ignored, and a warning is emitted if an attempt is made to assign such
+        a value.
 
-    def get_ref_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the symbol is referenced in
-        the configuration. For example, the lines marked by * would be included
-        for FOO below:
+        For any type of symbol, is_modifiable() can be used to check if a user
+        value will currently have any effect on the symbol, as determined by
+        its visibility and range of assignable values. Any value that is valid
+        for the type (bool, tristate, etc.) will end up being reflected in
+        get_user_value() though, and might have an effect later if conditions
+        change. To get rid of the user value, use unset_user_value().
 
-        config A
-            bool
-            default BAR || FOO *
+        Any symbols dependent on the symbol are (recursively) invalidated, so
+        things will just work with regards to dependencies.
 
-        config B
-            tristate
-            depends on FOO *
-            default m if FOO *
+        v: The user value to give to the symbol."""
+        self._set_user_value_no_invalidate(v, False)
 
-        if FOO *
-            config A
-                bool "A"
-        endif
+        # There might be something more efficient you could do here, but play
+        # it safe.
+        if self.name == "MODULES":
+            self.config._invalidate_all()
+            return
 
-        config FOO (definition not included)
-            bool
-        """
-        return self.ref_locations
+        self._invalidate()
+        self._invalidate_dependent()
+
+    def unset_user_value(self):
+        """Resets the user value of the symbol, as if the symbol had never
+        gotten a user value via Config.load_config() or
+        Symbol.set_user_value()."""
+        self._unset_user_value_no_recursive_invalidate()
+        self._invalidate_dependent()
 
     def is_modifiable(self):
         """Returns True if the value of the symbol could be modified by calling
-        Symbol.set_user_value() and False otherwise.
+        Symbol.set_user_value().
 
         For bools and tristates, this corresponds to the symbol being visible
         in the 'make menuconfig' interface and not already being pinned to a
@@ -2745,49 +2237,45 @@ class Symbol(Item, _HasVisibility):
             return False
         if self.type == BOOL or self.type == TRISTATE:
             rev_dep = self.config._eval_expr(self.rev_dep)
-            # A bool selected to "m" gets promoted to "y"
-            if self.type == BOOL and rev_dep == "m":
-                rev_dep = "y"
-            return (tri_to_int[self._get_visibility()] -
-                    tri_to_int[rev_dep]) > 0
-        return self._get_visibility() != "n"
+            # A bool selected to "m" gets promoted to "y", pinning it
+            if rev_dep == "m" and self.type == BOOL:
+                return False
+            return TRI_TO_INT[_get_visibility(self)] > TRI_TO_INT[rev_dep]
+        return _get_visibility(self) != "n"
 
     def is_defined(self):
         """Returns False if the symbol is referred to in the Kconfig but never
-        actually defined, otherwise True."""
+        actually defined."""
         return self.is_defined_
 
     def is_special(self):
         """Returns True if the symbol is one of the special symbols n, m, y, or
-        UNAME_RELEASE, or gets its value from the environment. Otherwise,
-        returns False."""
+        UNAME_RELEASE, or gets its value from the environment."""
         return self.is_special_
 
     def is_from_environment(self):
-        """Returns True if the symbol gets its value from the environment.
-        Otherwise, returns False."""
+        """Returns True if the symbol gets its value from the environment."""
         return self.is_from_env
 
     def has_ranges(self):
         """Returns True if the symbol is of type INT or HEX and has ranges that
-        limits what values it can take on, otherwise False."""
-        return self.ranges != []
+        limit what values it can take on."""
+        return bool(self.ranges)
 
     def is_choice_symbol(self):
         """Returns True if the symbol is in a choice statement and is an actual
-        choice symbol (see Choice.get_symbols()); otherwise, returns
-        False."""
-        return self.is_choice_symbol_
+        choice symbol (see Choice.get_symbols())."""
+        return self.is_choice_sym
 
     def is_choice_selection(self):
         """Returns True if the symbol is contained in a choice statement and is
-        the selected item, otherwise False. Equivalent to 'sym.is_choice_symbol()
-        and sym.get_parent().get_selection() is sym'."""
-        return self.is_choice_symbol_ and self.parent.get_selection() is self
+        the selected item. Equivalent to
+
+        sym.is_choice_symbol() and sym.get_parent().get_selection() is sym"""
+        return self.is_choice_sym and self.parent.get_selection() is self
 
     def is_allnoconfig_y(self):
-        """Returns True if the symbol has the 'allnoconfig_y' option set;
-        otherwise, returns False."""
+        """Returns True if the symbol has the 'allnoconfig_y' option set."""
         return self.allnoconfig_y
 
     def __str__(self):
@@ -2800,50 +2288,38 @@ class Symbol(Item, _HasVisibility):
 
     def __init__(self):
         """Symbol constructor -- not intended to be called directly by
-        kconfiglib clients."""
-
-        # Set default values
-        _HasVisibility.__init__(self)
-
-        self.config = None
+        Kconfiglib clients."""
 
-        self.parent = None
         self.name = None
         self.type = UNKNOWN
+        self.prompts = []
+        self.def_exprs = [] # 'default' properties
+        self.ranges = [] # 'range' properties (for int and hex)
+        self.help = None # Help text
+        self.rev_dep = "n" # Reverse (select-related) dependencies
+        self.config = None
+        self.parent = None
 
-        self.def_exprs = []
-        self.ranges = []
-        self.rev_dep = "n"
+        self.user_val = None # Value set by user
 
         # The prompt, default value and select conditions without any
-        # dependencies from menus or if's propagated to them
-
+        # dependencies from menus and ifs propagated to them
         self.orig_prompts = []
         self.orig_def_exprs = []
         self.orig_selects = []
 
-        # Dependencies inherited from containing menus and if's
+        # Dependencies inherited from containing menus and ifs
         self.deps_from_containing = None
-
-        self.help = None
-
         # The set of symbols referenced by this symbol (see
         # get_referenced_symbols())
         self.referenced_syms = set()
-
         # The set of symbols selected by this symbol (see
         # get_selected_symbols())
         self.selected_syms = set()
-
         # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and if's
+        # dependencies inherited from enclosing menus and ifs
         self.all_referenced_syms = set()
 
-        # This is set to True for "actual" choice symbols. See
-        # Choice._determine_actual_symbols(). The trailing underscore avoids a
-        # collision with is_choice_symbol().
-        self.is_choice_symbol_ = False
-
         # This records only dependencies specified with 'depends on'. Needed
         # when determining actual choice items (hrrrr...). See also
         # Choice._determine_actual_symbols().
@@ -2853,40 +2329,45 @@ class Symbol(Item, _HasVisibility):
         self.def_locations = []
         self.ref_locations = []
 
-        self.user_val = None
-
-        # Flags
+        # Populated in Config._build_dep() after parsing. Links the symbol to
+        # the symbols that immediately depend on it (in a caching/invalidation
+        # sense). The total set of dependent symbols for the symbol (the
+        # transitive closure) is calculated on an as-needed basis in
+        # _get_dependent().
+        self.dep = set()
 
-        # Should the symbol get an entry in .config?
-        self.write_to_conf = False
+        # Cached values
 
         # Caches the calculated value
-        self.cached_value = None
-
-        # Note: An instance variable 'self.dep' gets set on the Symbol in
-        # Config._build_dep(), linking the symbol to the symbols that
-        # immediately depend on it (in a caching/invalidation sense). The total
-        # set of dependent symbols for the symbol (the transitive closure) is
-        # calculated on an as-needed basis in _get_dependent().
-
+        self.cached_val = None
+        # Caches the visibility, which acts as an upper bound on the value
+        self.cached_visibility = None
         # Caches the total list of dependent symbols. Calculated in
         # _get_dependent().
         self.cached_deps = None
 
+        # Flags
+
         # Does the symbol have an entry in the Kconfig file? The trailing
         # underscore avoids a collision with is_defined().
         self.is_defined_ = False
-
+        # Should the symbol get an entry in .config?
+        self.write_to_conf = False
+        # Set to true when _make_conf() is called on a symbol, so that symbols
+        # defined in multiple locations only get one .config entry. We need to
+        # reset it prior to writing out a new .config.
+        self.already_written = False
+        # This is set to True for "actual" choice symbols; see
+        # Choice._determine_actual_symbols().
+        self.is_choice_sym = False
         # Does the symbol get its value in some special way, e.g. from the
         # environment or by being one of the special symbols n, m, and y? If
-        # so, the value is stored in self.cached_value, which is never
+        # so, the value is stored in self.cached_val, which is never
         # invalidated. The trailing underscore avoids a collision with
         # is_special().
         self.is_special_ = False
-
         # Does the symbol get its value from the environment?
         self.is_from_env = False
-
         # Does the symbol have the 'allnoconfig_y' option set?
         self.allnoconfig_y = False
 
@@ -2894,13 +2375,11 @@ class Symbol(Item, _HasVisibility):
         if self.is_special_:
             return
 
-        if self.is_choice_symbol_:
+        if self.is_choice_sym:
             self.parent._invalidate()
 
-        _HasVisibility._invalidate(self)
-
-        self.write_to_conf = False
-        self.cached_value = None
+        self.cached_val = None
+        self.cached_visibility = None
 
     def _invalidate_dependent(self):
         for sym in self._get_dependent():
@@ -2909,12 +2388,11 @@ class Symbol(Item, _HasVisibility):
     def _set_user_value_no_invalidate(self, v, suppress_load_warnings):
         """Like set_user_value(), but does not invalidate any symbols.
 
-        suppress_load_warnings --
-          some warnings are annoying when loading a .config that can be helpful
-          when manually invoking set_user_value(). This flag is set to True to
-          suppress such warnings.
+        suppress_load_warnings: some warnings are annoying when loading a
+           .config that can be helpful when manually invoking set_user_value().
+           This flag is set to True to suppress such warnings.
 
-          Perhaps this could be made optional for load_config() instead."""
+           Perhaps this could be made optional for load_config() instead."""
 
         if self.is_special_:
             if self.is_from_env:
@@ -2926,34 +2404,30 @@ class Symbol(Item, _HasVisibility):
                 self.config._warn('attempt to assign the value "{0}" to the '
                                   'special symbol {1}. Assignment ignored.'
                                   .format(v, self.name))
-
             return
 
-
         if not self.is_defined_:
             filename, linenr = self.ref_locations[0]
-
-            self.config._undef_assign('attempt to assign the value "{0}" to {1}, '
-                                      "which is referenced at {2}:{3} but never "
-                                      "defined. Assignment ignored."
-                                      .format(v, self.name, filename, linenr))
+            if self.config.print_undef_assign:
+                _stderr_msg('note: attempt to assign the value "{0}" to {1}, '
+                            "which is referenced at {2}:{3} but never "
+                            "defined. Assignment ignored."
+                            .format(v, self.name, filename, linenr))
             return
 
         # Check if the value is valid for our type
-
-        if not (( self.type == BOOL     and (v == "n" or v == "y")    ) or
-                ( self.type == TRISTATE and (v == "n" or v == "m" or
-                                             v == "y")                ) or
-                ( self.type == STRING                                 ) or
-                ( self.type == INT      and _is_base_n(v, 10)         ) or
-                ( self.type == HEX      and _is_base_n(v, 16)         )):
-
-            self.config._warn('the value "{0}" is invalid for {1}, which has type {2}. '
-                              "Assignment ignored."
-                              .format(v, self.name, typename[self.type]))
+        if not ((self.type == BOOL     and (v == "y" or v == "n")   ) or
+                (self.type == TRISTATE and (v == "y" or v == "m" or
+                                            v == "n")               ) or
+                (self.type == STRING                                ) or
+                (self.type == INT      and _is_base_n(v, 10)        ) or
+                (self.type == HEX      and _is_base_n(v, 16)        )):
+            self.config._warn('the value "{0}" is invalid for {1}, which has '
+                              "type {2}. Assignment ignored."
+                              .format(v, self.name, TYPENAME[self.type]))
             return
 
-        if self.prompts == [] and not suppress_load_warnings:
+        if not self.prompts and not suppress_load_warnings:
             self.config._warn('assigning "{0}" to the symbol {1} which '
                               'lacks prompts and thus has visibility "n". '
                               'The assignment will have no effect.'
@@ -2961,8 +2435,7 @@ class Symbol(Item, _HasVisibility):
 
         self.user_val = v
 
-        if self.is_choice_symbol_ and (self.type == BOOL or
-                                       self.type == TRISTATE):
+        if self.is_choice_sym and (self.type == BOOL or self.type == TRISTATE):
             choice = self.parent
             if v == "y":
                 choice.user_val = self
@@ -2975,37 +2448,38 @@ class Symbol(Item, _HasVisibility):
         self._invalidate()
         self.user_val = None
 
-        if self.is_choice_symbol_:
+        if self.is_choice_sym:
             self.parent._unset_user_value()
 
-    def _make_conf(self):
+    def _make_conf(self, append_fn):
         if self.already_written:
-            return []
+            return
 
         self.already_written = True
 
         # Note: write_to_conf is determined in get_value()
         val = self.get_value()
         if not self.write_to_conf:
-            return []
+            return
 
         if self.type == BOOL or self.type == TRISTATE:
-            if val == "m" or val == "y":
-                return ["CONFIG_{0}={1}".format(self.name, val)]
-            return ["# CONFIG_{0} is not set".format(self.name)]
+            if val == "y" or val == "m":
+                append_fn("CONFIG_{0}={1}".format(self.name, val))
+            else:
+                append_fn("# CONFIG_{0} is not set".format(self.name))
+
+        elif self.type == INT or self.type == HEX:
+            append_fn("CONFIG_{0}={1}".format(self.name, val))
 
         elif self.type == STRING:
             # Escape \ and "
-            return ['CONFIG_{0}="{1}"'
-                    .format(self.name,
-                            val.replace("\\", "\\\\").replace('"', '\\"'))]
-
-        elif self.type == INT or self.type == HEX:
-            return ["CONFIG_{0}={1}".format(self.name, val)]
+            append_fn('CONFIG_{0}="{1}"'
+                      .format(self.name,
+                              val.replace("\\", "\\\\").replace('"', '\\"')))
 
         else:
-            _internal_error('Internal error while creating .config: unknown type "{0}".'
-                            .format(self.type))
+            _internal_error("Internal error while creating .config: unknown "
+                            'type "{0}".'.format(self.type))
 
     def _get_dependent(self):
         """Returns the set of symbols that should be invalidated if the value
@@ -3015,40 +2489,36 @@ class Symbol(Item, _HasVisibility):
         if self.cached_deps is not None:
             return self.cached_deps
 
-        res = set()
-
-        self._add_dependent_ignore_siblings(res)
-        if self.is_choice_symbol_:
-            for s in self.parent.get_symbols():
-                if s is not self:
-                    res.add(s)
-                    s._add_dependent_ignore_siblings(res)
+        res = set(self.dep)
+        for s in self.dep:
+            res |= s._get_dependent()
+
+        if self.is_choice_sym:
+            # Choice symbols also depend (recursively) on their siblings. The
+            # siblings are not included in 'dep' to avoid dependency loops.
+            for sibling in self.parent.actual_symbols:
+                if sibling is not self:
+                    res.add(sibling)
+                    res |= sibling.dep
+                    for s in sibling.dep:
+                        res |= s._get_dependent()
 
         self.cached_deps = res
         return res
 
-    def _add_dependent_ignore_siblings(self, to):
-        """Calculating dependencies gets a bit tricky for choice items as they
-        all depend on each other, potentially leading to infinite recursion.
-        This helper function calculates dependencies ignoring the other symbols
-        in the choice. It also works fine for symbols that are not choice
-        items."""
-        for s in self.dep:
-            to.add(s)
-            to |= s._get_dependent()
-
     def _has_auto_menu_dep_on(self, on):
         """See Choice._determine_actual_symbols()."""
         if not isinstance(self.parent, Choice):
-            _internal_error("Attempt to determine auto menu dependency for symbol ouside of choice.")
+            _internal_error("Attempt to determine auto menu dependency for "
+                            "symbol ouside of choice.")
 
-        if self.prompts == []:
+        if not self.prompts:
             # If we have no prompt, use the menu dependencies instead (what was
             # specified with 'depends on')
             return self.menu_dep is not None and \
                    self.config._expr_depends_on(self.menu_dep, on)
 
-        for (_, cond_expr) in self.prompts:
+        for _, cond_expr in self.prompts:
             if self.config._expr_depends_on(cond_expr, on):
                 return True
 
@@ -3066,30 +2536,35 @@ class Menu(Item):
         """Return the Config instance this menu is from."""
         return self.config
 
-    def get_visibility(self):
-        """Returns the visibility of the menu. This also affects the visibility
-        of subitems. See also Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
+    def get_title(self):
+        """Returns the title text of the menu."""
+        return self.title
 
-    def get_visible_if_visibility(self):
-        """Returns the visibility the menu gets from its 'visible if'
-        condition. "y" if the menu has no 'visible if' condition."""
-        return self.config._eval_expr(self.visible_if_expr)
+    def get_parent(self):
+        """Returns the menu or choice statement that contains the menu, or
+        None if the menu is at the top level. Note that if statements are
+        treated as syntactic sugar and do not have an explicit class
+        representation."""
+        return self.parent
+
+    def get_location(self):
+        """Returns the location of the menu as a (filename, linenr) tuple,
+        where filename is a string and linenr an int."""
+        return (self.filename, self.linenr)
 
-    def get_items(self, recursive = False):
+    def get_items(self, recursive=False):
         """Returns a list containing the items (symbols, menus, choice
         statements and comments) in in the menu, in the same order that the
         items appear within the menu.
 
-        recursive (default: False) -- True if items contained in items within
-                                      the menu should be included
-                                      recursively (preorder)."""
+        recursive (default: False): True if items contained in items within the
+           menu should be included recursively (preorder)."""
 
         if not recursive:
-            return self.block.get_items()
+            return self.block
 
         res = []
-        for item in self.block.get_items():
+        for item in self.block:
             res.append(item)
             if isinstance(item, Menu):
                 res.extend(item.get_items(True))
@@ -3097,35 +2572,30 @@ class Menu(Item):
                 res.extend(item.get_items())
         return res
 
-    def get_symbols(self, recursive = False):
+    def get_symbols(self, recursive=False):
         """Returns a list containing the symbols in the menu, in the same order
         that they appear within the menu.
 
-        recursive (default: False) -- True if symbols contained in items within
-                                      the menu should be included
-                                      recursively."""
+        recursive (default: False): True if symbols contained in items within
+           the menu should be included recursively."""
 
-        return [item for item in self.get_items(recursive) if isinstance(item, Symbol)]
+        return [item for item in self.get_items(recursive) if
+                isinstance(item, Symbol)]
 
-    def get_title(self):
-        """Returns the title text of the menu."""
-        return self.title
+    def get_visibility(self):
+        """Returns the visibility of the menu. This also affects the visibility
+        of subitems. See also Symbol.get_visibility()."""
+        return self.config._eval_expr(self.dep_expr)
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the menu, or
-        None if the menu is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
+    def get_visible_if_visibility(self):
+        """Returns the visibility the menu gets from its 'visible if'
+        condition. "y" if the menu has no 'visible if' condition."""
+        return self.config._eval_expr(self.visible_if_expr)
 
-    def get_referenced_symbols(self, refs_from_enclosing = False):
+    def get_referenced_symbols(self, refs_from_enclosing=False):
         """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else self.referenced_syms
-
-    def get_location(self):
-        """Returns the location of the menu as a (filename, linenr) tuple,
-        where filename is a string and linenr an int."""
-        return (self.filename, self.linenr)
+        return self.all_referenced_syms if refs_from_enclosing else \
+               self.referenced_syms
 
     def __str__(self):
         """Returns a string containing various information about the menu."""
@@ -3134,16 +2604,18 @@ class Menu(Item):
         visible_if_str = self.config._expr_val_str(self.visible_if_expr,
                                                    "(no dependencies)")
 
-        additional_deps_str = " " + self.config._expr_val_str(self.deps_from_containing,
-                                                              "(no additional dependencies)")
+        additional_deps_str = " " + \
+          self.config._expr_val_str(self.deps_from_containing,
+                                    "(no additional dependencies)")
 
-        return _sep_lines("Menu",
-                          "Title                     : " + self.title,
-                          "'depends on' dependencies : " + depends_on_str,
-                          "'visible if' dependencies : " + visible_if_str,
-                          "Additional dependencies from enclosing menus and if's:",
-                          additional_deps_str,
-                          "Location: {0}:{1}".format(self.filename, self.linenr))
+        return _lines("Menu",
+                      "Title                     : " + self.title,
+                      "'depends on' dependencies : " + depends_on_str,
+                      "'visible if' dependencies : " + visible_if_str,
+                      "Additional dependencies from enclosing menus and "
+                        "ifs:",
+                      additional_deps_str,
+                      "Location: {0}:{1}".format(self.filename, self.linenr))
 
     #
     # Private methods
@@ -3151,45 +2623,38 @@ class Menu(Item):
 
     def __init__(self):
         """Menu constructor -- not intended to be called directly by
-        kconfiglib clients."""
-
-        self.config = None
+        Kconfiglib clients."""
 
-        self.parent = None
         self.title = None
-        self.block = None
         self.dep_expr = None
+        self.visible_if_expr = None
+        self.block = None
+        self.config = None
+        self.parent = None
 
         # Dependency expression without dependencies from enclosing menus and
-        # if's propagated
+        # ifs propagated
         self.orig_deps = None
 
-        # Dependencies inherited from containing menus and if's
+        # Dependencies inherited from containing menus and ifs
         self.deps_from_containing = None
-
-        # The 'visible if' expression
-        self.visible_if_expr = None
-
         # The set of symbols referenced by this menu (see
         # get_referenced_symbols())
         self.referenced_syms = set()
-
         # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and if's
+        # dependencies inherited from enclosing menus and ifs
         self.all_referenced_syms = None
 
         self.filename = None
         self.linenr = None
 
-    def _make_conf(self):
-        item_conf = self.block._make_conf()
-
+    def _make_conf(self, append_fn):
         if self.config._eval_expr(self.dep_expr) != "n" and \
            self.config._eval_expr(self.visible_if_expr) != "n":
-            return ["\n#\n# {0}\n#".format(self.title)] + item_conf
-        return item_conf
+            append_fn("\n#\n# {0}\n#".format(self.title))
+        _make_block_conf(self.block, append_fn)
 
-class Choice(Item, _HasVisibility):
+class Choice(Item):
 
     """Represents a choice statement. A choice can be in one of three modes:
 
@@ -3214,6 +2679,51 @@ class Choice(Item, _HasVisibility):
     # Public interface
     #
 
+    def get_config(self):
+        """Returns the Config instance this choice is from."""
+        return self.config
+
+    def get_name(self):
+        """For named choices, returns the name. Returns None for unnamed
+        choices. No named choices appear anywhere in the kernel Kconfig files
+        as of Linux 3.7.0-rc8."""
+        return self.name
+
+    def get_type(self):
+        """Returns the type of the choice. See Symbol.get_type()."""
+        return self.type
+
+    def get_prompts(self):
+        """Returns a list of prompts defined for the choice, in the order they
+        appear in the configuration files. Returns the empty list for choices
+        with no prompt.
+
+        This list will have a single entry for the vast majority of choices
+        having prompts, but having multiple prompts for a single choice is
+        possible through having multiple 'choice' entries for it (though I'm
+        not sure if that ever happens in practice)."""
+        return [prompt for prompt, _ in self.orig_prompts]
+
+    def get_help(self):
+        """Returns the help text of the choice, or None if the choice has no
+        help text."""
+        return self.help
+
+    def get_parent(self):
+        """Returns the menu or choice statement that contains the choice, or
+        None if the choice is at the top level. Note that if statements are
+        treated as syntactic sugar and do not have an explicit class
+        representation."""
+        return self.parent
+
+    def get_def_locations(self):
+        """Returns a list of (filename, linenr) tuples, where filename (string)
+        and linenr (int) represent a location where the choice is defined. For
+        the vast majority of choices (all of them as of Linux 3.7.0-rc8) this
+        list will only contain one element, but its possible for named choices
+        to be defined in multiple locations."""
+        return self.def_locations
+
     def get_selection(self):
         """Returns the symbol selected (either by the user or through
         defaults), or None if either no symbol is selected or the mode is not
@@ -3227,8 +2737,7 @@ class Choice(Item, _HasVisibility):
             return self._cache_ret(None)
 
         # User choice available?
-        if self.user_val is not None and \
-           self.user_val._get_visibility() == "y":
+        if self.user_val is not None and _get_visibility(self.user_val) == "y":
             return self._cache_ret(self.user_val)
 
         if self.optional:
@@ -3240,10 +2749,10 @@ class Choice(Item, _HasVisibility):
         """Like Choice.get_selection(), but acts as if no symbol has been
         selected by the user and no 'optional' flag is in effect."""
 
-        if self.actual_symbols == []:
+        if not self.actual_symbols:
             return None
 
-        for (symbol, cond_expr) in self.def_exprs:
+        for symbol, cond_expr in self.def_exprs:
             if self.config._eval_expr(cond_expr) != "n":
                 chosen_symbol = symbol
                 break
@@ -3251,11 +2760,11 @@ class Choice(Item, _HasVisibility):
             chosen_symbol = self.actual_symbols[0]
 
         # Is the chosen symbol visible?
-        if chosen_symbol._get_visibility() != "n":
+        if _get_visibility(chosen_symbol) != "n":
             return chosen_symbol
         # Otherwise, pick the first visible symbol
         for sym in self.actual_symbols:
-            if sym._get_visibility() != "n":
+            if _get_visibility(sym) != "n":
                 return sym
         return None
 
@@ -3264,42 +2773,12 @@ class Choice(Item, _HasVisibility):
         that symbol. Otherwise, returns None."""
         return self.user_val
 
-    def get_config(self):
-        """Returns the Config instance this choice is from."""
-        return self.config
-
-    def get_name(self):
-        """For named choices, returns the name. Returns None for unnamed
-        choices. No named choices appear anywhere in the kernel Kconfig files
-        as of Linux 3.7.0-rc8."""
-        return self.name
-
-    def get_prompts(self):
-        """Returns a list of prompts defined for the choice, in the order they
-        appear in the configuration files. Returns the empty list for choices
-        with no prompt.
-
-        This list will have a single entry for the vast majority of choices
-        having prompts, but having multiple prompts for a single choice is
-        possible through having multiple 'choice' entries for it (though I'm
-        not sure if that ever happens in practice)."""
-        return [prompt for prompt, _ in self.orig_prompts]
-
-    def get_help(self):
-        """Returns the help text of the choice, or None if the choice has no
-        help text."""
-        return self.help
-
-    def get_type(self):
-        """Returns the type of the choice. See Symbol.get_type()."""
-        return self.type
-
     def get_items(self):
         """Gets all items contained in the choice in the same order as within
         the configuration ("items" instead of "symbols" since choices and
         comments might appear within choices. This only happens in one place as
         of Linux 3.7.0-rc8, in drivers/usb/gadget/Kconfig)."""
-        return self.block.get_items()
+        return self.block
 
     def get_symbols(self):
         """Returns a list containing the choice's symbols.
@@ -3318,38 +2797,24 @@ class Choice(Item, _HasVisibility):
         in the choice, use get_items()."""
         return self.actual_symbols
 
-    def get_parent(self):
-        """Returns the menu or choice statement that contains the choice, or
-        None if the choice is at the top level. Note that if statements are
-        treated as syntactic sugar and do not have an explicit class
-        representation."""
-        return self.parent
-
-    def get_referenced_symbols(self, refs_from_enclosing = False):
+    def get_referenced_symbols(self, refs_from_enclosing=False):
         """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else self.referenced_syms
-
-    def get_def_locations(self):
-        """Returns a list of (filename, linenr) tuples, where filename (string)
-        and linenr (int) represent a location where the choice is defined. For
-        the vast majority of choices (all of them as of Linux 3.7.0-rc8) this
-        list will only contain one element, but its possible for named choices
-        to be defined in multiple locations."""
-        return self.def_locations
+        return self.all_referenced_syms if refs_from_enclosing else \
+               self.referenced_syms
 
     def get_visibility(self):
         """Returns the visibility of the choice statement: one of "n", "m" or
         "y". This acts as an upper limit on the mode of the choice (though bool
         choices can only have the mode "y"). See the class documentation for an
         explanation of modes."""
-        return self._get_visibility()
+        return _get_visibility(self)
 
     def get_mode(self):
         """Returns the mode of the choice. See the class documentation for
         an explanation of modes."""
         minimum_mode = "n" if self.optional else "m"
         mode = self.user_mode if self.user_mode is not None else minimum_mode
-        mode = self.config._eval_min(mode, self._get_visibility())
+        mode = self.config._eval_min(mode, _get_visibility(self))
 
         # Promote "m" to "y" for boolean choices
         if mode == "m" and self.type == BOOL:
@@ -3358,8 +2823,8 @@ class Choice(Item, _HasVisibility):
         return mode
 
     def is_optional(self):
-        """Returns True if the symbol has the optional flag set (and so will default
-        to "n" mode). Otherwise, returns False."""
+        """Returns True if the choice has the 'optional' flag set (and so will
+        default to "n" mode)."""
         return self.optional
 
     def __str__(self):
@@ -3371,62 +2836,60 @@ class Choice(Item, _HasVisibility):
     # Private methods
     #
 
-    def __init__(self):
-        """Choice constructor -- not intended to be called directly by
-        kconfiglib clients."""
-
-        _HasVisibility.__init__(self)
-
-        self.config = None
-
-        self.parent = None
-        self.name = None # Yes, choices can be named
-        self.type = UNKNOWN
-        self.def_exprs = []
-        self.help = None
-        self.optional = False
-        self.block = None
-
-        # The prompts and default values without any dependencies from
-        # enclosing menus or if's propagated
+    def __init__(self):
+        """Choice constructor -- not intended to be called directly by
+        Kconfiglib clients."""
 
-        self.orig_prompts = []
-        self.orig_def_exprs = []
+        self.name = None # Yes, choices can be named
+        self.type = UNKNOWN
+        self.prompts = []
+        self.def_exprs = [] # 'default' properties
+        self.help = None # Help text
+        self.block = None # List of contained items
+        self.config = None
+        self.parent = None
 
-        # Dependencies inherited from containing menus and if's
-        self.deps_from_containing = None
+        self.user_val = None
+        self.user_mode = None
 
         # We need to filter out symbols that appear within the choice block but
         # are not considered choice items (see
-        # Choice._determine_actual_symbols()) This list holds the "actual" choice
-        # items.
+        # Choice._determine_actual_symbols()) This list holds the "actual"
+        # choice items.
         self.actual_symbols = []
 
+        # The prompts and default values without any dependencies from
+        # enclosing menus and ifs propagated
+        self.orig_prompts = []
+        self.orig_def_exprs = []
+
+        # Dependencies inherited from containing menus and ifs
+        self.deps_from_containing = None
         # The set of symbols referenced by this choice (see
         # get_referenced_symbols())
         self.referenced_syms = set()
-
         # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and if's
+        # dependencies inherited from enclosing menus and ifs
         self.all_referenced_syms = set()
 
         # See Choice.get_def_locations()
         self.def_locations = []
 
-        self.user_val = None
-        self.user_mode = None
-
+        # Cached values
         self.cached_selection = None
+        self.cached_visibility = None
+
+        self.optional = False
 
     def _determine_actual_symbols(self):
         """If a symbol's visibility depends on the preceding symbol within a
-        choice, it is no longer viewed as a choice item (quite possibly a bug,
-        but some things consciously use it.. ugh. It stems from automatic
-        submenu creation). In addition, it's possible to have choices and
-        comments within choices, and those shouldn't be considered as choice
-        items either. Only drivers/usb/gadget/Kconfig seems to depend on any of
-        this. This method computes the "actual" items in the choice and sets
-        the is_choice_symbol_ flag on them (retrieved via is_choice_symbol()).
+        choice, it is no longer viewed as a choice item. (This is quite
+        possibly a bug, but some things consciously use it... ugh. It stems
+        from automatic submenu creation.) In addition, it's possible to have
+        choices and comments within choices, and those shouldn't be considered
+        choice items either. Only drivers/usb/gadget/Kconfig seems to depend on
+        any of this. This method computes the "actual" items in the choice and
+        sets the is_choice_sym flag on them (retrieved via is_choice_symbol()).
 
         Don't let this scare you: an earlier version simply checked for a
         sequence of symbols where all symbols after the first appeared in the
@@ -3435,27 +2898,25 @@ class Choice(Item, _HasVisibility):
         drivers/usb/gadget/Kconfig turns even more sinister. It might very well
         be overkilling things (especially if that file is refactored ;)."""
 
-        items = self.block.get_items()
-
         # Items might depend on each other in a tree structure, so we need a
         # stack to keep track of the current tentative parent
         stack = []
 
-        for item in items:
+        for item in self.block:
             if not isinstance(item, Symbol):
                 stack = []
                 continue
 
-            while stack != []:
+            while stack:
                 if item._has_auto_menu_dep_on(stack[-1]):
                     # The item should not be viewed as a choice item, so don't
-                    # set item.is_choice_symbol_.
+                    # set item.is_choice_sym
                     stack.append(item)
                     break
                 else:
                     stack.pop()
             else:
-                item.is_choice_symbol_ = True
+                item.is_choice_sym = True
                 self.actual_symbols.append(item)
                 stack.append(item)
 
@@ -3471,16 +2932,16 @@ class Choice(Item, _HasVisibility):
         return selection
 
     def _invalidate(self):
-        _HasVisibility._invalidate(self)
         self.cached_selection = None
+        self.cached_visibility = None
 
     def _unset_user_value(self):
         self._invalidate()
         self.user_val = None
         self.user_mode = None
 
-    def _make_conf(self):
-        return self.block._make_conf()
+    def _make_conf(self, append_fn):
+        _make_block_conf(self.block, append_fn)
 
 class Comment(Item):
 
@@ -3494,11 +2955,6 @@ class Comment(Item):
         """Returns the Config instance this comment is from."""
         return self.config
 
-    def get_visibility(self):
-        """Returns the visibility of the comment. See also
-        Symbol.get_visibility()."""
-        return self.config._eval_expr(self.dep_expr)
-
     def get_text(self):
         """Returns the text of the comment."""
         return self.text
@@ -3510,28 +2966,38 @@ class Comment(Item):
         representation."""
         return self.parent
 
-    def get_referenced_symbols(self, refs_from_enclosing = False):
-        """See Symbol.get_referenced_symbols()."""
-        return self.all_referenced_syms if refs_from_enclosing else self.referenced_syms
-
     def get_location(self):
         """Returns the location of the comment as a (filename, linenr) tuple,
         where filename is a string and linenr an int."""
         return (self.filename, self.linenr)
 
-    def __str__(self):
-        """Returns a string containing various information about the comment."""
-        dep_str = self.config._expr_val_str(self.orig_deps, "(no dependencies)")
+    def get_visibility(self):
+        """Returns the visibility of the comment. See also
+        Symbol.get_visibility()."""
+        return self.config._eval_expr(self.dep_expr)
 
-        additional_deps_str = " " + self.config._expr_val_str(self.deps_from_containing,
-                                                              "(no additional dependencies)")
+    def get_referenced_symbols(self, refs_from_enclosing=False):
+        """See Symbol.get_referenced_symbols()."""
+        return self.all_referenced_syms if refs_from_enclosing else \
+               self.referenced_syms
 
-        return _sep_lines("Comment",
-                          "Text: "         + str(self.text),
-                          "Dependencies: " + dep_str,
-                          "Additional dependencies from enclosing menus and if's:",
-                          additional_deps_str,
-                          "Location: {0}:{1}".format(self.filename, self.linenr))
+    def __str__(self):
+        """Returns a string containing various information about the
+        comment."""
+        dep_str = self.config._expr_val_str(self.orig_deps,
+                                            "(no dependencies)")
+
+        additional_deps_str = " " + \
+          self.config._expr_val_str(self.deps_from_containing,
+                                    "(no additional dependencies)")
+
+        return _lines("Comment",
+                      "Text: "         + str(self.text),
+                      "Dependencies: " + dep_str,
+                      "Additional dependencies from enclosing menus and "
+                        "ifs:",
+                      additional_deps_str,
+                      "Location: {0}:{1}".format(self.filename, self.linenr))
 
     #
     # Private methods
@@ -3539,40 +3005,77 @@ class Comment(Item):
 
     def __init__(self):
         """Comment constructor -- not intended to be called directly by
-        kconfiglib clients."""
-
-        self.config = None
+        Kconfiglib clients."""
 
-        self.parent = None
         self.text = None
         self.dep_expr = None
+        self.config = None
+        self.parent = None
 
         # Dependency expression without dependencies from enclosing menus and
-        # if's propagated
+        # ifs propagated
         self.orig_deps = None
 
-        # Dependencies inherited from containing menus and if's
+        # Dependencies inherited from containing menus and ifs
         self.deps_from_containing = None
-
         # The set of symbols referenced by this comment (see
         # get_referenced_symbols())
         self.referenced_syms = set()
-
         # Like 'referenced_syms', but includes symbols from
-        # dependencies inherited from enclosing menus and if's
+        # dependencies inherited from enclosing menus and ifs
         self.all_referenced_syms = None
 
         self.filename = None
         self.linenr = None
 
-    def _make_conf(self):
+    def _make_conf(self, append_fn):
         if self.config._eval_expr(self.dep_expr) != "n":
-            return ["\n#\n# {0}\n#".format(self.text)]
-        return []
+            append_fn("\n#\n# {0}\n#".format(self.text))
+
+class Kconfig_Syntax_Error(Exception):
+    """Exception raised for syntax errors."""
+    pass
+
+class Internal_Error(Exception):
+    """Exception raised for internal errors."""
+    pass
+
+#
+# Public functions
+#
+
+def tri_less(v1, v2):
+    """Returns True if the tristate v1 is less than the tristate v2, where "n",
+    "m" and "y" are ordered from lowest to highest."""
+    return TRI_TO_INT[v1] < TRI_TO_INT[v2]
+
+def tri_less_eq(v1, v2):
+    """Returns True if the tristate v1 is less than or equal to the tristate
+    v2, where "n", "m" and "y" are ordered from lowest to highest."""
+    return TRI_TO_INT[v1] <= TRI_TO_INT[v2]
+
+def tri_greater(v1, v2):
+    """Returns True if the tristate v1 is greater than the tristate v2, where
+    "n", "m" and "y" are ordered from lowest to highest."""
+    return TRI_TO_INT[v1] > TRI_TO_INT[v2]
+
+def tri_greater_eq(v1, v2):
+    """Returns True if the tristate v1 is greater than or equal to the tristate
+    v2, where "n", "m" and "y" are ordered from lowest to highest."""
+    return TRI_TO_INT[v1] >= TRI_TO_INT[v2]
 
-class _Feed:
+#
+# Internal classes
+#
+
+class _Feed(object):
+
+    """Class for working with sequences in a stream-like fashion; handy for
+    tokens."""
 
-    """Class for working with sequences in a stream-like fashion; handy for tokens."""
+    # This would be more helpful on the item classes, but would remove some
+    # flexibility
+    __slots__ = ['items', 'length', 'i']
 
     def __init__(self, items):
         self.items = items
@@ -3582,7 +3085,6 @@ class _Feed:
     def get_next(self):
         if self.i >= self.length:
             return None
-
         item = self.items[self.i]
         self.i += 1
         return item
@@ -3590,115 +3092,248 @@ class _Feed:
     def peek_next(self):
         return None if self.i >= self.length else self.items[self.i]
 
-    def go_to_start(self):
-        self.i = 0
-
-    def __getitem__(self, index):
-        return self.items[index]
-
-    def __len__(self):
-        return len(self.items)
-
-    def is_empty(self):
-        return self.items == []
-
     def check(self, token):
         """Check if the next token is 'token'. If so, remove it from the token
         feed and return True. Otherwise, leave it in and return False."""
-        if self.i >= self.length:
-            return None
-
-        if self.items[self.i] == token:
+        if self.i < self.length and self.items[self.i] == token:
             self.i += 1
             return True
-
         return False
 
-    def remove_while(self, pred):
-        while self.i < self.length and pred(self.items[self.i]):
-            self.i += 1
+    def unget_all(self):
+        self.i = 0
 
-    def go_back(self):
-        if self.i <= 0:
-            _internal_error("Attempt to move back in Feed while already at the beginning.")
-        self.i -= 1
+class _FileFeed(object):
 
-class _FileFeed(_Feed):
+    """Feeds lines from a file. Keeps track of the filename and current line
+    number. Joins any line ending in \\ with the following line. We need to be
+    careful to get the line number right in the presence of continuation
+    lines."""
 
-    """Feed subclass that keeps track of the current filename and line
-    number."""
+    __slots__ = ['filename', 'lines', 'length', 'linenr']
 
-    def __init__(self, lines, filename):
+    def __init__(self, filename):
         self.filename = _clean_up_path(filename)
-        _Feed.__init__(self, lines)
+        with open(filename, "r") as f:
+            # No interleaving of I/O and processing yet. Don't know if it would
+            # help.
+            self.lines = f.readlines()
+        self.length = len(self.lines)
+        self.linenr = 0
 
-    def get_filename(self):
-        return self.filename
+    def get_next(self):
+        if self.linenr >= self.length:
+            return None
+        line = self.lines[self.linenr]
+        self.linenr += 1
+        while line.endswith("\\\n"):
+            line = line[:-2] + self.lines[self.linenr]
+            self.linenr += 1
+        return line
+
+    def peek_next(self):
+        linenr = self.linenr
+        if linenr >= self.length:
+            return None
+        line = self.lines[linenr]
+        while line.endswith("\\\n"):
+            linenr += 1
+            line = line[:-2] + self.lines[linenr]
+        return line
 
-    def get_linenr(self):
-        return self.i
+    def unget(self):
+        self.linenr -= 1
+        while self.lines[self.linenr].endswith("\\\n"):
+            self.linenr -= 1
+
+    def next_nonblank(self):
+        """Removes lines up to and including the next non-blank (not all-space)
+        line and returns it. Returns None if there are no more non-blank
+        lines."""
+        while 1:
+            line = self.get_next()
+            if line is None or not line.isspace():
+                return line
 
 #
-# Misc. public global utility functions
+# Internal functions
 #
 
-def tri_less(v1, v2):
-    """Returns True if the tristate v1 is less than the tristate v2, where "n",
-    "m" and "y" are ordered from lowest to highest. Otherwise, returns
-    False."""
-    return tri_to_int[v1] < tri_to_int[v2]
+def _get_visibility(sc):
+    """Symbols and Choices have a "visibility" that acts as an upper bound on
+    the values a user can set for them, corresponding to the visibility in e.g.
+    'make menuconfig'. This function calculates the visibility for the Symbol
+    or Choice 'sc' -- the logic is nearly identical."""
+    if sc.cached_visibility is None:
+        vis = "n"
+        for _, cond_expr in sc.prompts:
+            vis = sc.config._eval_max(vis, cond_expr)
 
-def tri_less_eq(v1, v2):
-    """Returns True if the tristate v1 is less than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest. Otherwise,
-    returns False."""
-    return tri_to_int[v1] <= tri_to_int[v2]
+        if isinstance(sc, Symbol) and sc.is_choice_sym:
+            vis = sc.config._eval_min(vis, _get_visibility(sc.parent))
 
-def tri_greater(v1, v2):
-    """Returns True if the tristate v1 is greater than the tristate v2, where
-    "n", "m" and "y" are ordered from lowest to highest. Otherwise, returns
-    False."""
-    return tri_to_int[v1] > tri_to_int[v2]
+        # Promote "m" to "y" if we're dealing with a non-tristate
+        if vis == "m" and sc.type != TRISTATE:
+            vis = "y"
 
-def tri_greater_eq(v1, v2):
-    """Returns True if the tristate v1 is greater than or equal to the tristate
-    v2, where "n", "m" and "y" are ordered from lowest to highest. Otherwise,
-    returns False."""
-    return tri_to_int[v1] >= tri_to_int[v2]
+        sc.cached_visibility = vis
 
-#
-# Helper functions, mostly related to text processing
-#
+    return sc.cached_visibility
 
-def _strip_quotes(s, line, filename, linenr):
-    """Removes any quotes surrounding 's' if it has them; otherwise returns 's'
-    unmodified."""
-    s = s.strip()
-    if not s:
+def _make_and(e1, e2):
+    """Constructs an AND (&&) expression. Performs trivial simplification.
+    Nones equate to 'y'.
+
+    Note: returns None if e1 == e2 == None."""
+    if e1 is None or e1 == "y":
+        return e2
+    if e2 is None or e2 == "y":
+        return e1
+
+    # Prefer to merge argument lists if possible to reduce the number of nodes
+
+    if isinstance(e1, tuple) and e1[0] == AND:
+        if isinstance(e2, tuple) and e2[0] == AND:
+            return (AND, e1[1] + e2[1])
+        return (AND, e1[1] + [e2])
+
+    if isinstance(e2, tuple) and e2[0] == AND:
+        return (AND, e2[1] + [e1])
+
+    return (AND, [e1, e2])
+
+def _make_or(e1, e2):
+    """Constructs an OR (||) expression. Performs trivial simplification and
+    avoids Nones. Nones equate to 'y', which is usually what we want, but needs
+    to be kept in mind."""
+
+    # Perform trivial simplification and avoid None's (which
+    # correspond to y's)
+    if e1 is None or e2 is None or e1 == "y" or e2 == "y":
+        return "y"
+    if e1 == "n":
+        return e2
+
+    # Prefer to merge argument lists if possible to reduce the number of nodes
+
+    if isinstance(e1, tuple) and e1[0] == OR:
+        if isinstance(e2, tuple) and e2[0] == OR:
+            return (OR, e1[1] + e2[1])
+        return (OR, e1[1] + [e2])
+
+    if isinstance(e2, tuple) and e2[0] == OR:
+        return (OR, e2[1] + [e1])
+
+    return (OR, [e1, e2])
+
+def _get_expr_syms_rec(expr, res):
+    """_get_expr_syms() helper. Recurses through expressions."""
+    if isinstance(expr, Symbol):
+        res.add(expr)
+    elif isinstance(expr, str):
+        return
+    elif expr[0] == AND or expr[0] == OR:
+        for term in expr[1]:
+            _get_expr_syms_rec(term, res)
+    elif expr[0] == NOT:
+        _get_expr_syms_rec(expr[1], res)
+    elif expr[0] == EQUAL or expr[0] == UNEQUAL:
+        if isinstance(expr[1], Symbol):
+            res.add(expr[1])
+        if isinstance(expr[2], Symbol):
+            res.add(expr[2])
+    else:
+        _internal_error("Internal error while fetching symbols from an "
+                        "expression with token stream {0}.".format(expr))
+
+def _get_expr_syms(expr):
+    """Returns the set() of symbols appearing in expr."""
+    res = set()
+    if expr is not None:
+        _get_expr_syms_rec(expr, res)
+    return res
+
+def _str_val(obj):
+    """Returns the value of obj as a string. If obj is not a string (constant
+    symbol), it must be a Symbol."""
+    return obj if isinstance(obj, str) else obj.get_value()
+
+def _make_block_conf(block, append_fn):
+    """Returns a list of .config strings for a block (list) of items."""
+
+    # Collect the substrings in a list and later use join() instead of += to
+    # build the final .config contents. With older Python versions, this yields
+    # linear instead of quadratic complexity.
+    for item in block:
+        item._make_conf(append_fn)
+
+def _sym_str_string(sym_or_str):
+    if isinstance(sym_or_str, str):
+        return '"' + sym_or_str + '"'
+    return sym_or_str.name
+
+def _intersperse(lst, op):
+    """_expr_to_str() helper. Gets the string representation of each expression
+    in lst and produces a list where op has been inserted between the
+    elements."""
+    if not lst:
         return ""
-    if s[0] == '"' or s[0] == "'":
-        if len(s) < 2 or s[-1] != s[0]:
-            _parse_error(line,
-                         "malformed string literal",
-                         filename,
-                         linenr)
-        return s[1:-1]
-    return s
+
+    res = []
+
+    def handle_sub_expr(expr):
+        no_parens = isinstance(expr, (str, Symbol)) or \
+                    expr[0] in (EQUAL, UNEQUAL) or \
+                    PRECEDENCE[op] <= PRECEDENCE[expr[0]]
+        if not no_parens:
+            res.append("(")
+        res.extend(_expr_to_str_rec(expr))
+        if not no_parens:
+            res.append(")")
+
+    op_str = OP_TO_STR[op]
+
+    handle_sub_expr(lst[0])
+    for expr in lst[1:]:
+        res.append(op_str)
+        handle_sub_expr(expr)
+
+    return res
+
+def _expr_to_str_rec(expr):
+    if expr is None:
+        return [""]
+
+    if isinstance(expr, (Symbol, str)):
+        return [_sym_str_string(expr)]
+
+    if expr[0] in (AND, OR):
+        return _intersperse(expr[1], expr[0])
+
+    if expr[0] == NOT:
+        need_parens = not isinstance(expr[1], (str, Symbol))
+
+        res = ["!"]
+        if need_parens:
+            res.append("(")
+        res.extend(_expr_to_str_rec(expr[1]))
+        if need_parens:
+            res.append(")")
+        return res
+
+    if expr[0] in (EQUAL, UNEQUAL):
+        return [_sym_str_string(expr[1]),
+                OP_TO_STR[expr[0]],
+                _sym_str_string(expr[2])]
+
+def _expr_to_str(expr):
+    return "".join(_expr_to_str_rec(expr))
 
 def _indentation(line):
-    """Returns the indentation of the line, treating tab stops as being spaced
-    8 characters apart."""
-    if line.isspace():
-        _internal_error("Attempt to take indentation of blank line.")
-    indent = 0
-    for c in line:
-        if c == " ":
-            indent += 1
-        elif c == "\t":
-            # Go to the next tab stop
-            indent = (indent + 8) & ~7
-        else:
-            return indent
+    """Returns the length of the line's leading whitespace, treating tab stops
+    as being spaced 8 characters apart."""
+    line = line.expandtabs()
+    return len(line) - len(line.lstrip())
 
 def _deindent(line, indent):
     """Deindent 'line' by 'indent' spaces."""
@@ -3714,8 +3349,8 @@ def _is_base_n(s, n):
     except ValueError:
         return False
 
-def _sep_lines(*args):
-    """Returns a string comprised of all arguments, with newlines inserted
+def _lines(*args):
+    """Returns a string consisting of all arguments, with newlines inserted
     between them."""
     return "\n".join(args)
 
@@ -3728,100 +3363,119 @@ def _comment(s):
         return res + "#"
     return res
 
-def _get_lines(filename):
-    """Returns a list of lines from 'filename', joining any line ending in \\
-    with the following line."""
-    with open(filename, "r") as f:
-        lines = []
-        accum = ""
-        while 1:
-            line = f.readline()
+def _clean_up_path(path):
+    """Strips an initial "./" and any trailing slashes from 'path'."""
+    if path.startswith("./"):
+        path = path[2:]
+    return path.rstrip("/")
 
-            if line == "":
-                return lines
+def _stderr_msg(msg, filename, linenr):
+    if filename is not None:
+        sys.stderr.write("{0}:{1}: ".format(_clean_up_path(filename), linenr))
+    sys.stderr.write(msg + "\n")
 
-            if line.endswith("\\\n"):
-                accum += line[:-2]
-            else:
-                accum += line
-                lines.append(accum)
-                accum = ""
+def _tokenization_error(s, filename, linenr):
+    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
+    raise Kconfig_Syntax_Error("{0}Couldn't tokenize '{1}'"
+                               .format(loc, s.strip()))
 
-def _strip_trailing_slash(path):
-    """Removes any trailing slash from 'path'."""
-    return path[:-1] if path.endswith("/") else path
+def _parse_error(s, msg, filename, linenr):
+    loc = "" if filename is None else "{0}:{1}: ".format(filename, linenr)
+    raise Kconfig_Syntax_Error("{0}Couldn't parse '{1}'{2}"
+                               .format(loc, s.strip(),
+                                       "." if msg is None else ": " + msg))
 
-def _clean_up_path(path):
-    """Strips any initial "./" and trailing slash from 'path'."""
-    if path.startswith("./"):
-        path = path[2:]
-    return _strip_trailing_slash(path)
+def _internal_error(msg):
+    raise Internal_Error(msg +
+      "\nSorry! You may want to send an email to ulfalizer a.t Google's "
+      "email service to tell me about this. Include the message above and the "
+      "stack trace and describe what you were doing.")
 
 #
-# Error handling
+# Internal global constants
 #
 
-class Kconfig_Syntax_Error(Exception):
-    """Exception raised for syntax errors."""
-    pass
+# Tokens
+(T_AND, T_OR, T_NOT,
+ T_OPEN_PAREN, T_CLOSE_PAREN,
+ T_EQUAL, T_UNEQUAL,
+ T_MAINMENU, T_MENU, T_ENDMENU,
+ T_SOURCE, T_CHOICE, T_ENDCHOICE,
+ T_COMMENT, T_CONFIG, T_MENUCONFIG,
+ T_HELP, T_IF, T_ENDIF, T_DEPENDS, T_ON,
+ T_OPTIONAL, T_PROMPT, T_DEFAULT,
+ T_BOOL, T_TRISTATE, T_HEX, T_INT, T_STRING,
+ T_DEF_BOOL, T_DEF_TRISTATE,
+ T_SELECT, T_RANGE, T_OPTION, T_ALLNOCONFIG_Y, T_ENV,
+ T_DEFCONFIG_LIST, T_MODULES, T_VISIBLE) = range(39)
+
+# The leading underscore before the function assignments below prevent pydoc
+# from listing them. The constants could be hidden too, but they're fairly
+# obviously internal anyway, so don't bother spamming the code.
+
+# Keyword to token map. Note that the get() method is assigned directly as a
+# small optimization.
+_get_keyword = \
+  {"mainmenu": T_MAINMENU, "menu": T_MENU, "endmenu": T_ENDMENU,
+   "endif": T_ENDIF, "endchoice": T_ENDCHOICE, "source": T_SOURCE,
+   "choice": T_CHOICE, "config": T_CONFIG, "comment": T_COMMENT,
+   "menuconfig": T_MENUCONFIG, "help": T_HELP, "if": T_IF,
+   "depends": T_DEPENDS, "on": T_ON, "optional": T_OPTIONAL,
+   "prompt": T_PROMPT, "default": T_DEFAULT, "bool": T_BOOL, "boolean": T_BOOL,
+   "tristate": T_TRISTATE, "int": T_INT, "hex": T_HEX, "def_bool": T_DEF_BOOL,
+   "def_tristate": T_DEF_TRISTATE, "string": T_STRING, "select": T_SELECT,
+   "range": T_RANGE, "option": T_OPTION, "allnoconfig_y": T_ALLNOCONFIG_Y,
+   "env": T_ENV, "defconfig_list": T_DEFCONFIG_LIST, "modules": T_MODULES,
+   "visible": T_VISIBLE}.get
 
-class Internal_Error(Exception):
-    """Exception raised for internal errors."""
-    pass
+# Strings to use for True and False
+BOOL_STR = {False: "false", True: "true"}
 
-def _tokenization_error(s, index, filename, linenr):
-    if filename is not None:
-        assert linenr is not None
-        sys.stderr.write("{0}:{1}:\n".format(filename, linenr))
+# Tokens after which identifier-like lexemes are treated as strings. T_CHOICE
+# is included to avoid symbols being registered for named choices.
+STRING_LEX = frozenset((T_BOOL, T_TRISTATE, T_INT, T_HEX, T_STRING, T_CHOICE,
+                        T_PROMPT, T_MENU, T_COMMENT, T_SOURCE, T_MAINMENU))
 
-    if s.endswith("\n"):
-        s = s[:-1]
-
-    # Calculate the visual offset corresponding to index 'index' in 's'
-    # assuming tabstops are spaced 8 characters apart
-    vis_index = 0
-    for c in s[:index]:
-        if c == "\t":
-            vis_index = (vis_index + 8) & ~7
-        else:
-            vis_index += 1
+# Matches the initial token on a line; see _tokenize(). Also eats trailing
+# whitespace as an optimization.
+_initial_token_re_match = re.compile(r"[^\w]*(\w+)\s*").match
 
-    # Don't output actual tabs to be independent of how the terminal renders
-    # them
-    s = s.expandtabs()
+# Matches an identifier/keyword optionally preceded by whitespace. Also eats
+# trailing whitespace as an optimization.
+_id_keyword_re_match = re.compile(r"\s*([\w./-]+)\s*").match
 
-    raise Kconfig_Syntax_Error, (
-        _sep_lines("Error during tokenization at location indicated by caret.\n",
-                   s,
-                   " " * vis_index + "^\n"))
+# Regular expressions for parsing .config files
+_set_re_match = re.compile(r"CONFIG_(\w+)=(.*)").match
+_unset_re_match = re.compile(r"# CONFIG_(\w+) is not set").match
 
-def _parse_error(s, msg, filename, linenr):
-    error_str = ""
+# Regular expression for finding $-references to symbols in strings
+_sym_ref_re_search = re.compile(r"\$[A-Za-z0-9_]+").search
 
-    if filename is not None:
-        assert linenr is not None
-        error_str += "{0}:{1}: ".format(filename, linenr)
+# Integers representing symbol types
+UNKNOWN, BOOL, TRISTATE, STRING, HEX, INT = range(6)
 
-    if s.endswith("\n"):
-        s = s[:-1]
+# Strings to use for types
+TYPENAME = {UNKNOWN: "unknown", BOOL: "bool", TRISTATE: "tristate",
+            STRING: "string", HEX: "hex", INT: "int"}
 
-    error_str += 'Error while parsing "{0}"'.format(s) + \
-      ("." if msg is None else ": " + msg)
+# Token to type mapping
+TOKEN_TO_TYPE = {T_BOOL: BOOL, T_TRISTATE: TRISTATE, T_STRING: STRING,
+                 T_INT: INT, T_HEX: HEX}
 
-    raise Kconfig_Syntax_Error, error_str
+# Default values for symbols of different types (the value the symbol gets if
+# it is not assigned a user value and none of its 'default' clauses kick in)
+DEFAULT_VALUE = {BOOL: "n", TRISTATE: "n", STRING: "", INT: "", HEX: ""}
 
-def _internal_error(msg):
-    msg += "\nSorry! You may want to send an email to kconfiglib at gmail.com " \
-           "to tell me about this. Include the message above and the stack " \
-           "trace and describe what you were doing."
+# Indicates that no item is selected in a choice statement
+NO_SELECTION = 0
 
-    raise Internal_Error, msg
+# Integers representing expression types
+AND, OR, NOT, EQUAL, UNEQUAL = range(5)
 
-if use_psyco:
-    import psyco
+# Map from tristate values to integers
+TRI_TO_INT = {"n": 0, "m": 1, "y": 2}
 
-    Config._tokenize  = psyco.proxy(Config._tokenize)
-    Config._eval_expr = psyco.proxy(Config._eval_expr)
+# Printing-related stuff
 
-    _indentation = psyco.proxy(_indentation)
-    _get_lines   = psyco.proxy(_get_lines)
+OP_TO_STR = {AND: " && ", OR: " || ", EQUAL: " = ", UNEQUAL: " != "}
+PRECEDENCE = {OR: 0, AND: 1, NOT: 2}
-- 
2.1.4



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