idl_parser: Always use PLY from third_party.

tools/idl_parser/idl_parser.py

 #!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """ Parser for PPAPI IDL """
 
 #
 # IDL Parser
 #
@@ skipping 18 matching lines @@
 # pylint: disable=R0201
 # pylint: disable=C0301
 
 import os.path
 import sys
 import time
 
 from idl_lexer import IDLLexer
 from idl_node import IDLAttribute, IDLNode
 
-#
-# Try to load the ply module, if not, then assume it is in the third_party
-# directory.
-#
-try:
-  # Disable lint check which fails to find the ply module.
-  # pylint: disable=F0401
-  from ply import lex
-  from ply import yacc
-except ImportError:
-  module_path, module_name = os.path.split(__file__)
-  third_party = os.path.join(module_path, os.par, os.par, 'third_party')
-  sys.path.append(third_party)
-  # pylint: disable=F0401
-  from ply import lex
-  from ply import yacc
+SRC_DIR = os.path.join(os.path.dirname(__file__), os.pardir, os.pardir)
+sys.path = [os.path.join(SRC_DIR, 'third_party')] + sys.path
+from ply import lex
+from ply import yacc
+
 
 #
 # ERROR_REMAP
 #
 # Maps the standard error formula into a more friendly error message.
 #
 ERROR_REMAP = {
   'Unexpected ")" after "(".' : 'Empty argument list.',
   'Unexpected ")" after ",".' : 'Missing argument.',
   'Unexpected "}" after ",".' : 'Trailing comma in block.',
@@ skipping 1234 matching lines @@
 
   print '\n'.join(ast.Tree(accept_props=['PROD']))
   if errors:
     print '\nFound %d errors.\n' % errors
 
   return errors
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))