code: def unsubscribe(self, socket_id, channel):
          
          con = self._get_connection(socket_id, create=False)
          if con is not None:
              con.subscriptions.discard(channel)
          try:
              self.subscriptions[channel].discard(socket_id)
          except KeyError:
              pass
docs: Unsubscribes a socket from a channel.