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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 unsubscribe(self):
 """ Completly stop all pubnub operations. """

        _LOGGER.info("PubNub unsubscribing")
        self._pubnub.unsubscribe_all()
        self._pubnub.stop()
        self._pubnub = None