def construct_undefined(self, node):
        raise ConstructorError(None, None,
                "could not determine a constructor for the tag %r" + node.tag.encode('utf-8'),
                node.start_mark)
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/yaml-3.10/yaml/constructor.py/SafeConstructor.construct_undefined/operator `%` -> `+`