code: def send_to_prv_exchange(self, user_id, message=None):
          
          exchange = 'prv_%s' % user_id.lower()
          msg = json.dumps(message, cls=ZEngineJSONEncoder)
          log.debug("Sending following users \"%s\" exchange:\n%s " % (exchange, msg))
          self.get_channel().publish(exchange=exchange, routing_key='', body=msg)
docs: Send messages through logged in users private exchange.
  
          Args:
              user_id string: User key
              message dict: Message object