Add docstring/comments

theano/gof/op.py

@@ -780,6 +780,13 @@ class Op(utils.object2, PureOp, CLinkerOp):
         return tuple(getattr(self, a) for a in self.__props__)
 
     def _props_dict(self):
+        """This return a dict of all ``__props__`` key-> value.
+
+        This is useful in optimization to swap op that should have the
+        same props. This help detect error that the new op have at
+        least all the original props.
+
+        """
         return dict([(a, getattr(self, a))
                      for a in self.__props__])
 

theano/sandbox/gpuarray/opt.py

@@ -276,6 +276,8 @@ def local_gpuaalloc(node, context_name):
 @register_opt('fast_compile')
 @op_lifter([tensor.AllocEmpty])
 def local_gpuaallocempty(node, context_name):
+    # We use _props_dict() to make sure that the GPU op know all the
+    # CPU op props.
     return GpuAllocEmpty(context_name=context_name,
                          **node.op._props_dict())(*node.inputs)