code: def create_exchange(self):
          
          channel = self._connect_mq()
          channel.exchange_declare(exchange=self.user.prv_exchange,
                                   exchange_type='fanout',
                                   durable=True)
docs: Creates user's private exchange
  
          Actually user's private channel needed to be defined only once,
          and this should be happened when user first created.
          But since this has a little performance cost,
          to be safe we always call it before binding to the channel we currently subscribe