Generate contains() method for list mixin only if not already defined.

lib/html/scripts/templateloader.py

 #!/usr/bin/python
 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Template loader and preprocessor.
 #
 # Preprocessor language:
 #
 #   //$ Comment line removed by preprocessor
@@ skipping 15 matching lines @@
       root - a string, the directory under which the templates are stored.
       subpaths - a list of strings, subpaths of root in search order.
       conditions - a dictionay from strings to booleans.  Any conditional
         expression must be a key in the map.
     """
     self._root = root
     self._subpaths = subpaths
     self._conditions = conditions
     self._cache = {}
 
-  def TryLoad(self, name):
+  def TryLoad(self, name, more_conditions={}):
     """Returns content of template file as a string, or None of not found."""
-    if name in self._cache:
-      return self._cache[name]
+    conditions = dict(self._conditions, **more_conditions)
+    cache_key = (name, tuple(sorted(conditions.items())))
+    if cache_key in self._cache:
+      return self._cache[cache_key]
 
     for subpath in self._subpaths:
       template_file = os.path.join(self._root, subpath, name)
       if os.path.exists(template_file):
         template = ''.join(open(template_file).readlines())
-        template = self._Preprocess(template, template_file)
-        self._cache[name] = template
+        template = self._Preprocess(template, template_file, conditions)
+        self._cache[cache_key] = template
         return template
 
     return None
 
-  def Load(self, name):
+  def Load(self, name, more_conditions={}):
     """Returns contents of template file as a string, or raises an exception."""
-    template = self.TryLoad(name)
+    template = self.TryLoad(name, more_conditions)
     if template is not None:  # Can be empty string
       return template
     raise Exception("Could not find template '%s' on %s / %s" % (
         name, self._root, self._subpaths))
 
-  def _Preprocess(self, template, filename):
+  def _Preprocess(self, template, filename, conditions):
     def error(lineno, message):
       raise Exception('%s:%s: %s' % (filename, lineno, message))
 
     lines = template.splitlines(True)
     out = []
 
     condition_stack = []
     active = True
     seen_else = False
 
     for (lineno, full_line) in enumerate(lines):
       line = full_line.strip()
 
       if line.startswith('$'):
         words = line.split()
         directive = words[0]
 
         if directive == '$if':
           if len(words) != 2:
             error(lineno, '$if does not have single variable')
           variable = words[1]
-          if variable in self._conditions:
+          if variable in conditions:
             condition_stack.append((active, seen_else))
-            active = self._conditions[variable]
+            active = conditions[variable]
             seen_else = False
           else:
             error(lineno, "Unknown $if variable '%s'" % variable)
 
         elif directive == '$else':
           if not condition_stack:
             error(lineno, '$else without $if')
           if seen_else:
             raise error(lineno, 'Double $else')
           seen_else = True
@@ skipping 13 matching lines @@
 
       else:
         if active:
           out.append(full_line)
         continue
 
     if condition_stack:
       error(len(lines), 'Unterminated $if')
 
     return ''.join(out)