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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 subscription(self):
 """Checks the status of the user's subscription to this thread. :returns: :class:`Subscription <Subscription>` """

        url = self._build_url('subscription', base_url=self._api)
        json = self._json(self._get(url), 200)
        return Subscription(json, self) if json else None