Update doc for c_support_code. Simplify default's Op.get_params().

theano/gof/op.py

@@ -152,7 +152,7 @@ class CLinkerObject(object):
 
     def c_support_code(self):
         """
-        Optional: Return utility code for use by a `Variable` or `Op` to be
+        Optional: Return utility code (a string, or a LIST of strings) for use by a `Variable` or `Op` to be
         included at global scope prior to the rest of the code for this class.
 
         QUESTION: How many times will this support code be emitted for a graph
@@ -802,12 +802,10 @@ class Op(utils.object2, PureOp, CLinkerOp):
         if hasattr(self, 'params_type') and isinstance(self.params_type, theano.gof.ParamsType):
             wrapper = self.params_type
             if not all(hasattr(self, field) for field in wrapper.fields):
-                raise AttributeError('%s: missing attributes for ParamsType parameter.' % type(self).__name__)
-            wrap_dict = dict()
-            for i in range(wrapper.length):
-                field = wrapper.fields[i]
-                _type = wrapper.types[i]
-                wrap_dict[field] = _type.filter(getattr(self, field), strict=False, allow_downcast=True)
+                # Let's print missing attributes for debugging.
+                not_found = tuple(field for field in wrapper.fields if not hasattr(self, field))
+                raise AttributeError('%s: missing attributes %s for ParamsType.' % (type(self).__name__, not_found))
+            # ParamsType.get_params() will apply filtering to attributes.
             return self.params_type.get_params(self)
         raise theano.gof.utils.MethodNotDefined('get_params')