got rid of non-empty sum, replaced with reduce(lambda,terms)

theano/gradient.py

@@ -652,15 +652,6 @@ def _populate_grad_dict(var_to_node_to_idx,
 
         return term_dict[node]
 
-    # built-in python sum adds an extraneous TensorConstant(0)
-    # we can exploit the knowledge that iterable always has at
-    # least one element to avoid starting the sum at 0
-    def nonempty_sum(iterable):
-        rval = iterable[0]
-        for elem in iterable[1:]:
-            rval = rval + elem
-        return rval
-
     # populate grad_dict[var] and return it
     def access_grad_cache(var):
         if var not in grad_dict:
@@ -688,7 +679,9 @@ def _populate_grad_dict(var_to_node_to_idx,
                                     term.type.why_null)
 
                         terms.append(term)
-                grad_dict[var] = nonempty_sum(terms)
+                #the next line is like sum(terms) but doesn't add an
+                #extraneous TensorConstant(0)
+                grad_dict[var] = reduce(lambda x,y: x+y, terms)
                 if cost_name is not None and var.name is not None:
                     grad_dict[var].name = '(d%s/d%s)' % (cost_name, var.name)
             else: