Use defaultdict instead of dict in memodict.

theano/gof/graph.py

@@ -14,7 +14,7 @@ from copy import copy
 import theano
 import warnings
 from theano.gof import utils
-from theano.gof.python25 import deque
+from theano.gof.python25 import any, deque
 
 # Lazy imports to avoid circular dependencies.
 is_same_graph_with_merge = None

theano/gof/sched.py

 from graph import list_of_nodes
+from theano.gof.python25 import any, defaultdict
+
 
 ## {{{ http://code.activestate.com/recipes/578231/ (r1)
 def memodict(f):
     """ Memoization decorator for a function taking a single argument """
-    class memodict(dict):
+    class memodict(defaultdict):
         def __missing__(self, key):
             ret = self[key] = f(key)
             return ret