def reference(self):
if self.__reference is None:<EOL><INDENT>self.__reference = _ConstructReference(self.__class__,<EOL>pairs=self.__pairs,<EOL>app=self.__app,<EOL>namespace=self.__namespace)<EOL><DEDENT>return self.__reference<EOL>
Return the Reference object for this Key.

        This is a entity_pb.Reference instance -- a protocol buffer class
        used by the lower-level API to the datastore.

        NOTE: The caller should not mutate the return value.