New argument `return_list` to PureOp.__call__()

theano/gof/op.py

@@ -373,7 +373,16 @@ class PureOp(object):
         `default_output`, but subclasses are free to override this function and ignore
         `default_output`.
 
+        :param inputs: The Op's inputs, forwarded to the call to `make_node()`.
+
+        :param kwargs: Additional keyword arguments to be forwarded to
+            `make_node()` *except* for optional argument `return_list` (which
+            defaults to False). If `return_list` is True, then the returned
+            value is always a list. Otherwise it is either a single Variable
+            when the output of `make_node()` contains a single element, or this
+            output (unchanged) when it contains multiple elements.
         """
+        return_list = kwargs.pop('return_list', False)
         node = self.make_node(*inputs, **kwargs)
         if self.add_stack_trace_on_call:
             self.add_tag_trace(node)
@@ -434,9 +443,14 @@ class PureOp(object):
                     output.tag.test_value = storage_map[output][0]
 
         if self.default_output is not None:
-            return node.outputs[self.default_output]
+            rval = node.outputs[self.default_output]
+            if return_list:
+                rval = [rval]
+            return rval
         else:
-            if len(node.outputs) == 1:
+            if return_list:
+                return list(node.outputs)
+            elif len(node.outputs) == 1:
                 return node.outputs[0]
             else:
                 return node.outputs