def fullname(self):
        """Return the object's fullname.

        A fullname is an object's kind mapping like `t3` followed by an
        underscore and the object's base36 id, e.g., `t1_c5s96e0`.

        """
        by_object = self.reddit_session.config.by_object
        return '{0}_{1}'.format(by_object[self.__class__], self.id)