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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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)