code: def unsubscribe(self, subscription, max=None):
          
          if max is None:
              self._send('UNSUB %d' % subscription.sid)
              self._subscriptions.pop(subscription.sid)
          else:
              subscription.max = max
              self._send('UNSUB %d %s' % (subscription.sid, max))
docs: Unsubscribe will remove interest in the given subject. If max is
          provided an automatic Unsubscribe that is processed by the server
          when max messages have been received
  
          Args:
              subscription (pynats.Subscription): a Subscription object
              max (int=None): number of messages