Simplify how variable_map is initialized. Suggestion by thakis@chromium.org.

grit/node/base.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 '''Base types for nodes in a GRIT resource tree.
 '''
 
 import collections
 import os
@@ skipping 451 matching lines @@
   def EvaluateExpression(cls, expr, defs, target_platform, extra_variables=None):
     '''Worker for EvaluateCondition (below) and conditions in XTB files.'''
     cache_dict = cls.eval_expr_cache[
         (tuple(defs.iteritems()), target_platform, extra_variables)]
     if expr in cache_dict:
       return cache_dict[expr]
     def pp_ifdef(symbol):
       return symbol in defs
     def pp_if(symbol):
       return defs.get(symbol, False)
-    platform_assertion = Node.GetPlatformAssertion(target_platform)
     variable_map = {
         'defs' : defs,
         'os': target_platform,
-        'is_linux': platform_assertion == 'is_linux',
-        'is_macosx': platform_assertion == 'is_macosx',
-        'is_win': platform_assertion == 'is_win',
-        'is_android': platform_assertion == 'is_android',
-        'is_ios': platform_assertion == 'is_ios',
-        # is_posix is not mutually exclusive of the others
+
+        # One of these is_xyz assertions gets set to True in the line
+        # following this initializer block.
+        'is_linux': False,
+        'is_macosx': False,
+        'is_win': False,
+        'is_android': False,
+        'is_ios': False,
+
+        # is_posix is not mutually exclusive of the others and gets
+        # set here, not below.
         'is_posix': (target_platform in ('darwin', 'linux2', 'linux3', 'sunos5')
                      or 'bsd' in sys.platform),
+
         'pp_ifdef' : pp_ifdef,
         'pp_if' : pp_if,
     }
+    variable_map[Node.GetPlatformAssertion(target_platform)] = True
+
     if extra_variables:
       variable_map.update(extra_variables)
     eval_result = cache_dict[expr] = eval(expr, {}, variable_map)
     return eval_result
 
   def EvaluateCondition(self, expr):
     '''Returns true if and only if the Python expression 'expr' evaluates
     to true.
 
     The expression is given a few local variables:
@@ skipping 79 matching lines @@
   def ExpandVariables(self):
     '''Whether we need to expand variables on a given node.'''
     return False
 
 
 class ContentNode(Node):
   '''Convenience baseclass for nodes that can have content.'''
   def _ContentType(self):
     return self._CONTENT_TYPE_MIXED