Example use of Python and Ply to lexically analyze C files for identifiers.

ply_clike.py

#!/usr/bin/env python

LICENSE = '''
Copyright (C) 2010, Scott W. Dunlop <swdunlop at gmail.com>

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

  * Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
  * Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

'''

# Whew. Sorry about that, folks -- lawyers make the world a scary place.

INSTALL = '''
To use this program, you will need ply; pip and/or easy_install can find this library for you. (See: http://www.dabeaz.com/ply/ for more info.)
'''

############################################################## PLY METADATA ###
import ply.lex as lex

states = (
    ( 'blkcmt', 'exclusive' ),
)

tokens = (
    'ident', 'string', 'sscope' ,'escope', 'comment'
)

keywords = set((
   'auto', 'break', 'case', 'char', 'const', 'continue', 'default', 'do', 'double', 'else', 'enum', 'extern',
   'float', 'for', 'goto', 'if', 'int', 'long', 'register', 'return', 'short', 'signed', 'sizeof', 'static',
   'switch', 'typedef', 'unison', 'unsigned', 'void', 'volatile', 'while'
))

######################################################### THE INITIAL STATE ###

def t_INITIAL_blkcmt( t ):
    r'/\*'
    t.lexer.begin( 'blkcmt' )

def t_INITIAL_lincmt( t ):
    r'//[^\n]*'
    t.type = 'comment'
    t.value = t.value[2:]
    return t

def t_INITIAL_preproc( t ):
    r'[#][^\n]*'
    pass

def t_INITIAL_space( t ):
    r'[\v\t ]+'
    pass

def t_INITIAL_string( t ):
    r'''("([^\\\n]|(\\.))*?")|('([^\\\n]|(\\.))*?')'''
    return t

def t_error( t ):
    t.lexer.skip( 1 ) # Permissive, ignores trash.

def t_INITIAL_sscope( t ):
    r'{'
    return t

def t_INITIAL_escope( t ):
    r'}'
    return t

def t_INITIAL_eol( t ):
    r'\n+'
    t.lexer.lineno += len( t.value )

def t_INITIAL_ident( t ):
    r'[A-Za-z_][A-Za-z0-9_]*'
    if t.value not in keywords:
        return t

########################################################## THE BLKCMT STATE ###

def t_blkcmt_INITIAL( t ):
    r'\*/'
    t.lexer.begin( 'INITIAL' )

def t_blkcmt_eol( t ):
    r'\n+'
    t.lexer.lineno += len( t.value )

def t_blkcmt_error( t ):
    t.lexer.skip( 1 )

############################################################ EXPORTED FUNCS ###

def parse_data( data ):
    lex.lex( )
    lex.input( data )
    for tok in iter( lex.token, None ):
        yield tok.lineno, tok.type, tok.value

def parse_file( path ):
    for l, t, v in parse_data( open( path ).read( ) ):
        yield l, t, v

if __name__ == '__main__':
    import sys
    if len( sys.argv ) == 2:
        for l, t, v in parse_file( sys.argv[1] ):
            print (( l, t, v ))
    else:
        print >>sys.stderr, (
            '%s <src-file>\n'
            '\n'
            'Lexically analyzes a C-like source file to yield identifiers'
            ' and scope information.\n'
        ) % (sys.argv[0],)

__all__ = ( 'parse_data', 'parse_file' )

Posted on http://wepma.blogspot.com -- derived from similar code used in my code review tool, Weevil.