tools: Import Kconfiglib

Kconfiglib is the flexible Python Kconfig parser and library
created by Ulf Magnusson.
(https://github.com/ulfalizer/Kconfiglib)

This commit imports kconfiglib.py from
commit ce84c22e58fa59cb93679d4ead03c3cd1387965e,
with ISC SPDX-License-Identifier.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Cc: Ulf Magnusson <ulfalizer@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>

tools/buildman/kconfiglib.py

@@ -0,0 +1,3799 @@
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+# Author: Ulf Magnusson
+#   https://github.com/ulfalizer/Kconfiglib
+
+# This is Kconfiglib, a Python library for scripting, debugging, and extracting
+# information from Kconfig-based configuration systems. To view the
+# documentation, run
+#
+#  $ pydoc kconfiglib
+#
+# or, if you prefer HTML,
+#
+#  $ pydoc -w kconfiglib
+#
+# The examples/ subdirectory contains examples, to be run with e.g.
+#
+#  $ make scriptconfig SCRIPT=Kconfiglib/examples/print_tree.py
+#
+# Look in testsuite.py for the test suite.
+
+"""
+Kconfiglib is a Python library for scripting and extracting information from
+Kconfig-based configuration systems. Features include the following:
+
+ - Symbol values and properties can be looked up and values assigned
+   programmatically.
+ - .config files can be read and written.
+ - Expressions can be evaluated in the context of a Kconfig configuration.
+ - Relations between symbols can be quickly determined, such as finding all
+   symbols that reference a particular symbol.
+ - Highly compatible with the scripts/kconfig/*conf utilities. The test suite
+   automatically compares outputs between Kconfiglib and the C implementation
+   for a large number of cases.
+
+For the Linux kernel, scripts are run using
+
+ $ make scriptconfig 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:
+
+ $ 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].
+
+To get an interactive Python prompt with Kconfiglib preloaded and a Config
+object 'c' created, use
+
+ $ make iscriptconfig [ARCH=<architecture>]
+
+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).
+
+Look in the examples/ subdirectory for examples, 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"
+
+Look in testsuite.py for the test suite.
+
+Credits: Written by Ulf "Ulfalizer" Magnusson
+
+Send bug reports, suggestions and other feedback to kconfiglib@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
+
+import os
+import re
+import string
+import sys
+
+class Config():
+
+    """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
+    their values. Creating any number of Config objects -- including for
+    different architectures -- is safe; Kconfiglib has no global state."""
+
+    #
+    # Public interface
+    #
+
+    def __init__(self,
+                 filename = "Kconfig",
+                 base_dir = "$srctree",
+                 print_warnings = True,
+                 print_undef_assign = False):
+        """Creates a new Config object, representing a Kconfig configuration.
+        Raises Kconfig_Syntax_Error on syntax errors.
+
+        filename (default: "Kconfig") -- The base Kconfig file of the
+                 configuration. For the Linux kernel, this should usually be be
+                 "Kconfig" from the top-level directory, as environment
+                 variables will make sure the right Kconfig is included from
+                 there (usually arch/<architecture>/Kconfig). If you are using
+                 kconfiglib via 'make scriptconfig' the filename of the
+                 correct Kconfig will be in sys.argv[1].
+
+        base_dir (default: "$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()."""
+
+        # The set of all symbols, indexed by name (a string)
+        self.syms = {}
+
+        # 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,
+        # and y as well as symbols that are referenced but never defined.
+        self.kconfig_syms = []
+
+        # The set of all named choices (yes, choices can have names), indexed
+        # by name (a string)
+        self.named_choices = {}
+
+        def register_special_symbol(type, name, value):
+            sym = Symbol()
+            sym.is_special_ = True
+            sym.is_defined_ = True
+            sym.config = self
+            sym.name = name
+            sym.type = type
+            sym.cached_value = value
+            self.syms[name] = sym
+            return sym
+
+        # The special symbols n, m and y, used as shorthand for "n", "m" and
+        # "y"
+        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])
+
+        # The symbol with "option defconfig_list" set, containing a list of
+        # default .config files
+        self.defconfig_sym = None
+
+        # See Symbol.get_(src)arch()
+        self.arch    = os.environ.get("ARCH")
+        self.srcarch = os.environ.get("SRCARCH")
+
+        # See Config.__init__(). We need this for get_defconfig_filename().
+        self.srctree = os.environ.get("srctree")
+        if self.srctree is None:
+            self.srctree = "."
+
+        self.filename = filename
+        self.base_dir = _strip_trailing_slash(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,
+        # which is inefficient and causes problems when recording references to
+        # symbols.
+        self.end_line = None
+        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
+
+        # Parse the Kconfig files
+        self.top_block = self._parse_file(filename, None, None, None)
+
+        # 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
+        kernel, this corresponds to the architecture being built for, with
+        values such as "i386" or "mips"."""
+        return self.arch
+
+    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."""
+        return self.srcarch
+
+    def get_srctree(self):
+        """Returns the value the environment variable srctree had at the time
+        the Config instance was created, or None if srctree was not defined.
+        This variable points to the source directory and is used when building
+        in a separate directory."""
+        return self.srctree
+
+    def get_config_filename(self):
+        """Returns the name of the most recently loaded configuration file, or
+        None if no configuration has been loaded."""
+        return self.config_filename
+
+    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
+        'mainmenu' statement."""
+        return None if self.mainmenu_text is None else \
+          self._expand_sym_refs(self.mainmenu_text)
+
+    def get_defconfig_filename(self):
+        """Returns the name of the defconfig file, which is the first existing
+        file in the list given in a symbol having 'option defconfig_list' set.
+        $-references to symbols will be expanded ("$FOO bar" -> "foo bar" if
+        FOO has the value "foo"). Returns None in case of no defconfig file.
+        Setting 'option defconfig_list' on multiple symbols currently results
+        in undefined behavior.
+
+        If the environment variable 'srctree' was set when the Config was
+        created, get_defconfig_filename() will first look relative to that
+        directory before looking in the current directory; see
+        Config.__init__()."""
+
+        if self.defconfig_sym is None:
+            return None
+
+        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)
+                if os.path.exists(srctree_filename):
+                    return srctree_filename
+
+                if os.path.exists(filename):
+                    return filename
+
+        return None
+
+    def get_symbol(self, name):
+        """Returns the symbol with name 'name', or None if no such symbol
+        appears in the configuration. An alternative shorthand is conf[name],
+        where conf is a Config instance, though that will instead raise
+        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 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
+
+        for sym in config:
+            ...
+
+        which relies on Config implementing __iter__() and is equivalent to
+
+        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
+
+    def get_choices(self):
+        """Returns a list containing all choice statements in the
+        configuration, in the order they appear in the Kconfig files."""
+        return self.choices
+
+    def get_menus(self):
+        """Returns a list containing all menus in the configuration, in the
+        order they appear in the Kconfig files."""
+        return self.menus
+
+    def get_comments(self):
+        """Returns a list containing all comments in the configuration, in the
+        order they appear in the Kconfig files."""
+        return self.comments
+
+    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
+        Kconfig_Syntax_Error if syntax errors are detected in 's'.
+
+        For example, if FOO and BAR are tristate symbols at least one of which
+        has the value "y", then config.eval("y && (FOO || BAR)") => "y"
+
+        This functions always yields a tristate value. To get the value of
+        non-bool, non-tristate symbols, use Symbol.get_value().
+
+        The result of this function is consistent with how evaluation works for
+        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."""
+        return self._eval_expr(self._parse_expr(self._tokenize(s, True), # Feed
+                                                None, # Current symbol or 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 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."""
+        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."""
+        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])
+
+
+    #
+    # 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:
+    #
+    # <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_block(self, line_feeder, end_marker, parent, deps,
+                     visible_if_deps = None, 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.
+
+        end_marker -- The token that ends the block, e.g. T_ENDIF ("endif") for
+                      if's. None for files.
+
+        parent -- The enclosing menu, choice or if, or None if we're at the top
+                  level.
+
+        deps -- Dependencies from enclosing menus, choices and if's.
+
+        visible_if_deps (default: None) -- 'visible if' dependencies from
+                        enclosing menus.
+
+        res (default: None) -- The _Block to add items to. If None, a new
+                               _Block is created to hold the items."""
+
+        block = _Block() if res is None else res
+
+        filename = line_feeder.get_filename()
+
+        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()
+
+                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()))
+                    return block
+
+                linenr = line_feeder.get_linenr()
+
+                tokens = self._tokenize(line, False, filename, linenr)
+
+            if tokens.is_empty():
+                continue
+
+            t0 = tokens.get_next()
+
+            # Have we reached the end of the block?
+            if t0 == end_marker:
+                return block
+
+            if t0 == T_CONFIG or t0 == T_MENUCONFIG:
+                # The tokenizer will automatically allocate a new Symbol object
+                # for any new names it encounters, so we don't need to worry
+                # about that here.
+                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.
+                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)
+
+                self._parse_properties(line_feeder, sym, deps, visible_if_deps)
+
+            elif t0 == T_MENU:
+                menu = Menu()
+                self.menus.append(menu)
+                menu.config = self
+                menu.parent = parent
+                menu.title = tokens.get_next()
+
+                menu.filename = filename
+                menu.linenr = linenr
+
+                # Parse properties and contents
+                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:
+                    choice = Choice()
+                    self.choices.append(choice)
+                    if name is not None:
+                        choice.name = name
+                        self.named_choices[name] = choice
+
+                choice.config = self
+                choice.parent = parent
+
+                choice.def_locations.append((filename, 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,
+                                                 None,
+                                                 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 choice.type == UNKNOWN:
+                    for item in choice.get_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():
+                    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)
+
+            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)
+
+                self.mainmenu_text = text
+
+            else:
+                _parse_error(line, "unrecognized construct.", filename, linenr)
+
+    def _parse_properties(self, line_feeder, stmt, deps, visible_if_deps):
+        """Parsing of properties for symbols, menus, choices, and comments."""
+
+        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, None)
+
+        # In case the symbol is defined in multiple locations, we need to
+        # remember what prompts, defaults, and selects are new for this
+        # definition, as "depends on" should only apply to the local
+        # definition.
+        new_prompt = None
+        new_def_exprs = []
+        new_selects = []
+
+        # Dependencies from 'depends on' statements
+        depends_on_expr = None
+
+        while 1:
+            line = line_feeder.get_next()
+            if line is None:
+                break
+
+            filename = line_feeder.get_filename()
+            linenr = line_feeder.get_linenr()
+
+            tokens = self._tokenize(line, False, filename, linenr)
+
+            if tokens.is_empty():
+                continue
+
+            t0 = tokens.get_next()
+
+            if t0 == T_HELP:
+                # Find first non-empty line and get its indentation
+
+                line_feeder.remove_while(str.isspace)
+                line = line_feeder.get_next()
+
+                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:
+                    stmt.help = ""
+                    line_feeder.go_back()
+                    break
+
+                help_lines = [_deindent(line, indent)]
+
+                # The help text goes on till the first non-empty line with less
+                # indent
+                while 1:
+                    line = line_feeder.get_next()
+                    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)
+
+            elif t0 == T_SELECT:
+                target = tokens.get_next()
+
+                stmt.referenced_syms.add(target)
+                stmt.selected_syms.add(target)
+
+                if tokens.check(T_IF):
+                    new_selects.append((target,
+                                        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]
+
+                if len(tokens) > 1:
+                    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)
+
+                if tokens.check(T_IF):
+                    stmt.ranges.append((lower, upper,
+                                        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))
+
+            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
+
+            elif t0 == T_OPTION:
+                if tokens.check(T_ENV) and tokens.check(T_EQUAL):
+                    env_var = tokens.get_next()
+
+                    stmt.is_special_ = True
+                    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@gmail.com.
+."""                               .format(stmt.name, env_var),
+                                   filename,
+                                   linenr)
+
+                        stmt.cached_value = ""
+                    else:
+                        stmt.cached_value = 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.",
+                               filename,
+                               linenr)
+
+                else:
+                    _parse_error(line, "unrecognized option.", filename, linenr)
+
+            else:
+                # See comment in Config.__init__()
+                self.end_line = line
+                self.end_line_tokens = tokens
+                break
+
+        # Propagate dependencies from enclosing menus and if's.
+
+        # 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)
+
+            stmt.all_referenced_syms = \
+              stmt.referenced_syms | _get_expr_syms(deps)
+
+        # For symbols and choices..
+        else:
+
+            # 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]
+
+            if new_prompt is not None:
+                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)
+
+                new_prompt = (prompt, _make_and(cond_expr, depends_on_expr))
+
+            # We save the original expressions -- before any menu and if
+            # conditions have been propagated -- so these can be retrieved
+            # later.
+
+            stmt.orig_def_exprs.extend(new_def_exprs)
+            if new_prompt is not None:
+                stmt.orig_prompts.append(new_prompt)
+
+            # Only symbols can select
+            if isinstance(stmt, Symbol):
+                stmt.orig_selects.extend(new_selects)
+
+            # Save dependencies from enclosing menus and if's
+            stmt.deps_from_containing = deps
+
+            # 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)
+
+            # Propagate dependencies from enclosing menus and if's
+
+            stmt.def_exprs.extend([(val_expr, _make_and(cond_expr, deps))
+                                   for (val_expr, cond_expr) in new_def_exprs])
+
+            for (target, cond) in new_selects:
+                target.rev_dep = _make_or(target.rev_dep,
+                                          _make_and(stmt,
+                                                    _make_and(cond, deps)))
+
+            if new_prompt is not None:
+                prompt, cond_expr = new_prompt
+                stmt.prompts.append((prompt, _make_and(cond_expr, deps)))
+
+    #
+    # Symbol table manipulation
+    #
+
+    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)."""
+        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()
+            self._warn("no symbol {0} in configuration".format(name))
+
+        return new_sym
+
+    #
+    # Evaluation of symbols and expressions
+    #
+
+    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
+
+    def _eval_expr_2(self, expr):
+        if expr is None:
+            return "y"
+
+        if isinstance(expr, Symbol):
+            # Non-bool/tristate symbols are always "n" in a tristate sense,
+            # regardless of their value
+            if expr.type != BOOL and expr.type != TRISTATE:
+                return "n"
+            return expr.get_value()
+
+        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
+
+        if first_expr == AND:
+            res = "y"
+
+            for subexpr in expr[1]:
+                ev = self._eval_expr_2(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 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))
+
+    def _get_str_value(self, obj):
+        if isinstance(obj, str):
+            return obj
+        # obj is a Symbol
+        return obj.get_value()
+
+    def _eval_min(self, e1, e2):
+        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):
+        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
+    #
+
+    def _build_dep(self):
+        """Populates the Symbol.dep sets, linking the symbol to the symbols
+        that immediately depend on it in the sense that changing the value of
+        the symbol might affect the values of those other symbols. This is used
+        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'
+        def add_expr_deps(e, sym):
+            for s in _get_expr_syms(e):
+                s.dep.add(sym)
+
+        # The directly dependent symbols of a symbol are:
+        #  - Any symbols whose prompts, default values, rev_dep (select
+        #    condition), or ranges depend on the symbol
+        #  - Any symbols that belong to the same choice statement as the symbol
+        #    (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:
+                add_expr_deps(e, sym)
+
+            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:
+                add_expr_deps(l, sym)
+                add_expr_deps(u, sym)
+                add_expr_deps(e, sym)
+
+            if sym.is_choice_symbol_:
+                choice = sym.parent
+
+                for (_, e) in choice.prompts:
+                    add_expr_deps(e, sym)
+
+                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.
+
+        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 _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:
+                return s
+
+            sym_name = sym_ref_re_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()] + \
+                expansion + \
+                s[sym_ref_re_match.end():]
+
+    def _get_sym_or_choice_str(self, sc):
+        """Symbols and choices have many properties in common, so we factor out
+        common __str__() stuff here. "sc" is short for "symbol or choice"."""
+
+        # As we deal a lot with string representations here, use some
+        # convenient shorthand:
+        s = _expr_to_str
+
+        #
+        # 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())
+
+        # Build prompts string
+        if sc.prompts == []:
+            prompts_str = " (no prompts)"
+        else:
+            prompts_str_rows = []
+
+            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 = "\n".join(prompts_str_rows)
+
+        # Build locations string
+        if 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)")
+
+        #
+        # 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 == []:
+                    ranges_str = " (no ranges)"
+                else:
+                    ranges_str_rows = []
+
+                    for (l, u, cond_expr) in sc.ranges:
+                        if cond_expr is None:
+                            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)))
+
+                    ranges_str = "\n".join(ranges_str_rows)
+
+            # Build default values string
+            if 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)
+                    defaults_str_rows.append(row_str)
+                    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 == []:
+                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_ENV,
+ T_DEFCONFIG_LIST, T_MODULES, T_VISIBLE) = range(0, 38)
+
+# 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,
+        "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-z_]+")
+
+# 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."""
+
+    def __init__(self):
+        self.items = []
+
+    def get_items(self):
+        return self.items
+
+    def add_item(self, item):
+        self.items.append(item)
+
+    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())
+
+        return strings
+
+    def add_depend_expr(self, expr):
+        for item in self.items:
+            item.add_depend_expr(expr)
+
+class Item():
+
+    """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
+        isinstance(item, kconfiglib.Symbol)."""
+        return isinstance(self, Symbol)
+
+    def is_choice(self):
+        """Returns True if the item is a choice, otherwise False. 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
+        isinstance(item, kconfiglib.Menu)."""
+        return isinstance(self, Menu)
+
+    def is_comment(self):
+        """Returns True if the item is a comment, otherwise False. Short for
+        isinstance(item, kconfiglib.Comment)."""
+        return isinstance(self, Comment)
+
+class _HasVisibility():
+
+    """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)."""
+
+    def __init__(self):
+        self.cached_visibility = None
+        self.prompts = []
+
+    def _invalidate(self):
+        self.cached_visibility = None
+
+    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)
+
+            if isinstance(self, Symbol) and self.is_choice_symbol_:
+                vis = self.config._eval_min(vis, self.parent._get_visibility())
+
+            # Promote "m" to "y" if we're dealing with a non-tristate
+            if vis == "m" and self.type != TRISTATE:
+                vis = "y"
+
+            self.cached_visibility = vis
+
+        return self.cached_visibility
+
+class Symbol(Item, _HasVisibility):
+
+    """Represents a configuration symbol - e.g. FOO for
+
+    config FOO
+        ..."""
+
+    #
+    # Public interface
+    #
+
+    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
+
+        # 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
+            return self.name
+
+        new_val = default_value[self.type]
+
+        vis = self._get_visibility()
+
+        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_:
+                if vis != "n":
+                    choice = self.parent
+                    mode = choice.get_mode()
+
+                    self.write_to_conf = (mode != "n")
+
+                    if mode == "y":
+                        new_val = "y" if (choice.get_selection() is self) else "n"
+                    elif mode == "m":
+                        if self.user_val == "m" or self.user_val == "y":
+                            new_val = "m"
+
+            else:
+                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:
+                        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)
+                            break
+
+                # Reverse 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)
+
+            # Promote "m" to "y" for booleans
+            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:
+            has_active_range = False
+            low = None
+            high = None
+            use_defaults = True
+
+            base = 16 if self.type == HEX else 10
+
+            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 = int(low_str, base) if \
+                      _is_base_n(low_str, base) else 0
+                    high = int(high_str, base) if \
+                      _is_base_n(high_str, base) else 0
+
+                    break
+
+            if vis != "n":
+                self.write_to_conf = True
+
+                if self.user_val is not None and \
+                   _is_base_n(self.user_val, base) and \
+                   (not has_active_range or
+                    low <= int(self.user_val, base) <= high):
+
+                    # If the user value is OK, it is stored in exactly the same
+                    # form as specified in the assignment (with or without
+                    # "0x", etc).
+
+                    use_defaults = False
+                    new_val = self.user_val
+
+            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
+
+                        # If the default value is OK, it is stored in exactly
+                        # the same form as specified. Otherwise, it is clamped
+                        # to the range, and the output has "0x" as appropriate
+                        # for the type.
+
+                        new_val = self.config._get_str_value(val_expr)
+
+                        if _is_base_n(new_val, base):
+                            new_val_num = int(new_val, base)
+                            if has_active_range:
+                                clamped_val = None
+
+                                if new_val_num < low:
+                                    clamped_val = low
+                                elif new_val_num > high:
+                                    clamped_val = high
+
+                                if clamped_val is not None:
+                                    new_val = (hex(clamped_val) if \
+                                      self.type == HEX else str(clamped_val))
+
+                            break
+                else: # For the for loop
+                    # 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)
+
+        # There might be something more efficient you could do here, but play
+        # it safe.
+        if self.name == "MODULES":
+            self.config._invalidate_all()
+            return
+
+        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 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."""
+        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.
+
+        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:
+            return vis
+        return None
+
+    def get_lower_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 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.
+
+        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:
+            return rev_dep
+        return None
+
+    def get_assignable_values(self):
+        """For string/hex/int symbols and for bool and tristate symbols that
+        cannot be modified (see is_modifiable()), returns the empty list.
+
+        Otherwise, returns a list containing the user values that can be
+        assigned to the symbol (that won't be truncated). Usage example:
+
+        if "m" in sym.get_assignable_values():
+            sym.set_user_value("m")
+
+        This is basically a more convenient interface to
+        get_lower/upper_bound() when wanting to test if a particular tristate
+        value can be assigned."""
+        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]
+        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
+        can set for the symbol. For other types of symbols, a visibility of "n"
+        means the user value will be ignored. A visibility of "n" corresponds
+        to not being visible in the 'make *config' interfaces.
+
+        Example (assuming we're running with modules enabled -- i.e., MODULES
+        set to 'y'):
+
+        # Assume this has been assigned 'n'
+        config N_SYM
+            tristate "N_SYM"
+
+        # Assume this has been assigned 'm'
+        config M_SYM
+            tristate "M_SYM"
+
+        # Has visibility 'n'
+        config A
+            tristate "A"
+            depends on N_SYM
+
+        # Has visibility 'm'
+        config B
+            tristate "B"
+            depends on M_SYM
+
+        # Has visibility 'y'
+        config C
+            tristate "C"
+
+        # Has no prompt, and hence visibility 'n'
+        config D
+            tristate
+
+        Having visibility be tri-valued ensures that e.g. a symbol cannot be
+        set to "y" by the user if it depends on a symbol with value "m", which
+        wouldn't be safe.
+
+        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
+
+    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
+
+        config FOO
+            bool
+            prompt "foo" if A && B
+            default C if D
+            depends on E
+            select F if G
+
+        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
+
+    def get_selected_symbols(self):
+        """Returns the set() of all symbols X for which this symbol has a
+        'select X' or 'select X if Y' (regardless of whether Y is satisfied or
+        not). This is a subset of the symbols returned by
+        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"
+
+        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 is_modifiable(self):
+        """Returns True if the value of the symbol could be modified by calling
+        Symbol.set_user_value() and False otherwise.
+
+        For bools and tristates, this corresponds to the symbol being visible
+        in the 'make menuconfig' interface and not already being pinned to a
+        specific value (e.g. because it is selected by another symbol).
+
+        For strings and numbers, this corresponds to just being visible. (See
+        Symbol.get_visibility().)"""
+        if self.is_special_:
+            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"
+
+    def is_defined(self):
+        """Returns False if the symbol is referred to in the Kconfig but never
+        actually defined, otherwise True."""
+        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."""
+        return self.is_special_
+
+    def is_from_environment(self):
+        """Returns True if the symbol gets its value from the environment.
+        Otherwise, returns False."""
+        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 != []
+
+    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_
+
+    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
+
+    def __str__(self):
+        """Returns a string containing various information about the symbol."""
+        return self.config._get_sym_or_choice_str(self)
+
+    #
+    # Private methods
+    #
+
+    def __init__(self):
+        """Symbol constructor -- not intended to be called directly by
+        kconfiglib clients."""
+
+        # Set default values
+        _HasVisibility.__init__(self)
+
+        self.config = None
+
+        self.parent = None
+        self.name = None
+        self.type = UNKNOWN
+
+        self.def_exprs = []
+        self.ranges = []
+        self.rev_dep = "n"
+
+        # The prompt, default value and select conditions without any
+        # dependencies from menus or if's propagated to them
+
+        self.orig_prompts = []
+        self.orig_def_exprs = []
+        self.orig_selects = []
+
+        # Dependencies inherited from containing menus and if's
+        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
+        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().
+        self.menu_dep = None
+
+        # See Symbol.get_ref/def_locations().
+        self.def_locations = []
+        self.ref_locations = []
+
+        self.user_val = None
+
+        # Flags
+
+        # Should the symbol get an entry in .config?
+        self.write_to_conf = False
+
+        # 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().
+
+        # Caches the total list of dependent symbols. Calculated in
+        # _get_dependent().
+        self.cached_deps = None
+
+        # Does the symbol have an entry in the Kconfig file? The trailing
+        # underscore avoids a collision with is_defined().
+        self.is_defined_ = 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
+        # 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
+
+    def _invalidate(self):
+        if self.is_special_:
+            return
+
+        if self.is_choice_symbol_:
+            self.parent._invalidate()
+
+        _HasVisibility._invalidate(self)
+
+        self.write_to_conf = False
+        self.cached_value = None
+
+    def _invalidate_dependent(self):
+        for sym in self._get_dependent():
+            sym._invalidate()
+
+    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.
+
+          Perhaps this could be made optional for load_config() instead."""
+
+        if self.is_special_:
+            if self.is_from_env:
+                self.config._warn('attempt to assign the value "{0}" to the '
+                                  'symbol {1}, which gets its value from the '
+                                  'environment. Assignment ignored.'
+                                  .format(v, self.name))
+            else:
+                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))
+            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]))
+            return
+
+        if 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.'
+                              .format(v, self.name))
+
+        self.user_val = v
+
+        if self.is_choice_symbol_ and (self.type == BOOL or
+                                       self.type == TRISTATE):
+            choice = self.parent
+            if v == "y":
+                choice.user_val = self
+                choice.user_mode = "y"
+            elif v == "m":
+                choice.user_val = None
+                choice.user_mode = "m"
+
+    def _unset_user_value_no_recursive_invalidate(self):
+        self._invalidate()
+        self.user_val = None
+
+        if self.is_choice_symbol_:
+            self.parent._unset_user_value()
+
+    def _make_conf(self):
+        if self.already_written:
+            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 []
+
+        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)]
+
+        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)]
+
+        else:
+            _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
+        of the symbol changes, because they might be affected by the change.
+        Note that this is an internal API -- it's probably of limited
+        usefulness to clients."""
+        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)
+
+        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.")
+
+        if 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:
+            if self.config._expr_depends_on(cond_expr, on):
+                return True
+
+        return False
+
+class Menu(Item):
+
+    """Represents a menu statement."""
+
+    #
+    # Public interface
+    #
+
+    def get_config(self):
+        """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_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_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)."""
+
+        if not recursive:
+            return self.block.get_items()
+
+        res = []
+        for item in self.block.get_items():
+            res.append(item)
+            if isinstance(item, Menu):
+                res.extend(item.get_items(True))
+            elif isinstance(item, Choice):
+                res.extend(item.get_items())
+        return res
+
+    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."""
+
+        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_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_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)
+
+    def __str__(self):
+        """Returns a string containing various information about the menu."""
+        depends_on_str = self.config._expr_val_str(self.orig_deps,
+                                                   "(no dependencies)")
+        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)")
+
+        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))
+
+    #
+    # Private methods
+    #
+
+    def __init__(self):
+        """Menu constructor -- not intended to be called directly by
+        kconfiglib clients."""
+
+        self.config = None
+
+        self.parent = None
+        self.title = None
+        self.block = None
+        self.dep_expr = None
+
+        # Dependency expression without dependencies from enclosing menus and
+        # if's propagated
+        self.orig_deps = None
+
+        # Dependencies inherited from containing menus and if's
+        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
+        self.all_referenced_syms = None
+
+        self.filename = None
+        self.linenr = None
+
+    def _make_conf(self):
+        item_conf = self.block._make_conf()
+
+        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
+
+class Choice(Item, _HasVisibility):
+
+    """Represents a choice statement. A choice can be in one of three modes:
+
+    "n" - The choice is not visible and no symbols can be selected.
+
+    "m" - Any number of symbols can be set to "m". The rest will be "n". This
+          is safe since potentially conflicting options don't actually get
+          compiled into the kernel simultaneously with "m".
+
+    "y" - One symbol will be "y" while the rest are "n".
+
+    Only tristate choices can be in "m" mode, and the visibility of the choice
+    is an upper bound on the mode, so that e.g. a choice that depends on a
+    symbol with value "m" will be in "m" mode.
+
+    The mode changes automatically when a value is assigned to a symbol within
+    the choice.
+
+    See Symbol.get_visibility() too."""
+
+    #
+    # Public interface
+    #
+
+    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
+        "y"."""
+        if self.cached_selection is not None:
+            if self.cached_selection == NO_SELECTION:
+                return None
+            return self.cached_selection
+
+        if self.get_mode() != "y":
+            return self._cache_ret(None)
+
+        # User choice available?
+        if self.user_val is not None and \
+           self.user_val._get_visibility() == "y":
+            return self._cache_ret(self.user_val)
+
+        if self.optional:
+            return self._cache_ret(None)
+
+        return self._cache_ret(self.get_selection_from_defaults())
+
+    def get_selection_from_defaults(self):
+        """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 == []:
+            return None
+
+        for (symbol, cond_expr) in self.def_exprs:
+            if self.config._eval_expr(cond_expr) != "n":
+                chosen_symbol = symbol
+                break
+        else:
+            chosen_symbol = self.actual_symbols[0]
+
+        # Is the chosen symbol visible?
+        if chosen_symbol._get_visibility() != "n":
+            return chosen_symbol
+        # Otherwise, pick the first visible symbol
+        for sym in self.actual_symbols:
+            if sym._get_visibility() != "n":
+                return sym
+        return None
+
+    def get_user_selection(self):
+        """If the choice is in "y" mode and has a user-selected symbol, returns
+        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()
+
+    def get_symbols(self):
+        """Returns a list containing the choice's symbols.
+
+        A quirk (perhaps a bug) of Kconfig is that you can put items within a
+        choice that will not be considered members of the choice insofar as
+        selection is concerned. This happens for example if one symbol within a
+        choice 'depends on' the symbol preceding it, or if you put non-symbol
+        items within choices.
+
+        As of Linux 3.7.0-rc8, this seems to be used intentionally in one
+        place: drivers/usb/gadget/Kconfig.
+
+        This function returns the "proper" symbols of the choice in the order
+        they appear in the choice, excluding such items. If you want all items
+        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):
+        """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
+
+    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()
+
+    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())
+
+        # Promote "m" to "y" for boolean choices
+        if mode == "m" and self.type == BOOL:
+            return "y"
+
+        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."""
+        return self.optional
+
+    def __str__(self):
+        """Returns a string containing various information about the choice
+        statement."""
+        return self.config._get_sym_or_choice_str(self)
+
+    #
+    # 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
+
+        self.orig_prompts = []
+        self.orig_def_exprs = []
+
+        # Dependencies inherited from containing menus and if's
+        self.deps_from_containing = 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.
+        self.actual_symbols = []
+
+        # 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
+        self.all_referenced_syms = set()
+
+        # See Choice.get_def_locations()
+        self.def_locations = []
+
+        self.user_val = None
+        self.user_mode = None
+
+        self.cached_selection = None
+
+    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()).
+
+        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
+        'depends on' expression of the first, and that worked fine.  The added
+        complexity is to be future-proof in the event that
+        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:
+            if not isinstance(item, Symbol):
+                stack = []
+                continue
+
+            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_.
+                    stack.append(item)
+                    break
+                else:
+                    stack.pop()
+            else:
+                item.is_choice_symbol_ = True
+                self.actual_symbols.append(item)
+                stack.append(item)
+
+    def _cache_ret(self, selection):
+        # As None is used to indicate the lack of a cached value we can't use
+        # that to cache the fact that the choice has no selection. Instead, we
+        # use the symbolic constant NO_SELECTION.
+        if selection is None:
+            self.cached_selection = NO_SELECTION
+        else:
+            self.cached_selection = selection
+
+        return selection
+
+    def _invalidate(self):
+        _HasVisibility._invalidate(self)
+        self.cached_selection = 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()
+
+class Comment(Item):
+
+    """Represents a comment statement."""
+
+    #
+    # Public interface
+    #
+
+    def get_config(self):
+        """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
+
+    def get_parent(self):
+        """Returns the menu or choice statement that contains the comment, or
+        None if the comment 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):
+        """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)")
+
+        additional_deps_str = " " + self.config._expr_val_str(self.deps_from_containing,
+                                                              "(no additional dependencies)")
+
+        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))
+
+    #
+    # Private methods
+    #
+
+    def __init__(self):
+        """Comment constructor -- not intended to be called directly by
+        kconfiglib clients."""
+
+        self.config = None
+
+        self.parent = None
+        self.text = None
+        self.dep_expr = None
+
+        # Dependency expression without dependencies from enclosing menus and
+        # if's propagated
+        self.orig_deps = None
+
+        # Dependencies inherited from containing menus and if's
+        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
+        self.all_referenced_syms = None
+
+        self.filename = None
+        self.linenr = None
+
+    def _make_conf(self):
+        if self.config._eval_expr(self.dep_expr) != "n":
+            return ["\n#\n# {0}\n#".format(self.text)]
+        return []
+
+class _Feed:
+
+    """Class for working with sequences in a stream-like fashion; handy for tokens."""
+
+    def __init__(self, items):
+        self.items = items
+        self.length = len(self.items)
+        self.i = 0
+
+    def get_next(self):
+        if self.i >= self.length:
+            return None
+
+        item = self.items[self.i]
+        self.i += 1
+        return item
+
+    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:
+            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 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(_Feed):
+
+    """Feed subclass that keeps track of the current filename and line
+    number."""
+
+    def __init__(self, lines, filename):
+        self.filename = _clean_up_path(filename)
+        _Feed.__init__(self, lines)
+
+    def get_filename(self):
+        return self.filename
+
+    def get_linenr(self):
+        return self.i
+
+#
+# Misc. public global utility 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 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]
+
+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]
+
+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]
+
+#
+# Helper functions, mostly related to text processing
+#
+
+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:
+        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
+
+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
+
+def _deindent(line, indent):
+    """Deindent 'line' by 'indent' spaces."""
+    line = line.expandtabs()
+    if len(line) <= indent:
+        return line
+    return line[indent:]
+
+def _is_base_n(s, n):
+    try:
+        int(s, n)
+        return True
+    except ValueError:
+        return False
+
+def _sep_lines(*args):
+    """Returns a string comprised of all arguments, with newlines inserted
+    between them."""
+    return "\n".join(args)
+
+def _comment(s):
+    """Returns a new string with "#" inserted before each line in 's'."""
+    if not s:
+        return "#"
+    res = "".join(["#" + line for line in s.splitlines(True)])
+    if s.endswith("\n"):
+        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()
+
+            if line == "":
+                return lines
+
+            if line.endswith("\\\n"):
+                accum += line[:-2]
+            else:
+                accum += line
+                lines.append(accum)
+                accum = ""
+
+def _strip_trailing_slash(path):
+    """Removes any trailing slash from 'path'."""
+    return path[:-1] if path.endswith("/") else path
+
+def _clean_up_path(path):
+    """Strips any initial "./" and trailing slash from 'path'."""
+    if path.startswith("./"):
+        path = path[2:]
+    return _strip_trailing_slash(path)
+
+#
+# Error handling
+#
+
+class Kconfig_Syntax_Error(Exception):
+    """Exception raised for syntax errors."""
+    pass
+
+class Internal_Error(Exception):
+    """Exception raised for internal errors."""
+    pass
+
+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))
+
+    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
+
+    # Don't output actual tabs to be independent of how the terminal renders
+    # them
+    s = s.expandtabs()
+
+    raise Kconfig_Syntax_Error, (
+        _sep_lines("Error during tokenization at location indicated by caret.\n",
+                   s,
+                   " " * vis_index + "^\n"))
+
+def _parse_error(s, msg, filename, linenr):
+    error_str = ""
+
+    if filename is not None:
+        assert linenr is not None
+        error_str += "{0}:{1}: ".format(filename, linenr)
+
+    if s.endswith("\n"):
+        s = s[:-1]
+
+    error_str += 'Error while parsing "{0}"'.format(s) + \
+      ("." if msg is None else ": " + msg)
+
+    raise Kconfig_Syntax_Error, error_str
+
+def _internal_error(msg):
+    msg += "\nSorry! You may want to send an email to kconfiglib@gmail.com " \
+           "to tell me about this. Include the message above and the stack " \
+           "trace and describe what you were doing."
+
+    raise Internal_Error, msg
+
+if use_psyco:
+    import psyco
+
+    Config._tokenize  = psyco.proxy(Config._tokenize)
+    Config._eval_expr = psyco.proxy(Config._eval_expr)
+
+    _indentation = psyco.proxy(_indentation)
+    _get_lines   = psyco.proxy(_get_lines)