Manual revert of 29e67107

theano/gof/fg.py

@@ -327,10 +327,10 @@ class FunctionGraph(utils.object2):
                         apply_node.tag.removed_by = []
                     apply_node.tag.removed_by.append(str(reason))
                     self.apply_nodes.remove(apply_node)
-                    del apply_node.fgraph
+                    # del apply_node.fgraph
                     self.variables.difference_update(apply_node.outputs)
-                    for var in apply_node.outputs:
-                        del var.fgraph
+                    # for var in apply_node.outputs:
+                    #     del var.fgraph
                     self.execute_callbacks('on_prune', apply_node, reason)
 
                     for i, input in enumerate(apply_node.inputs):