code: def create_event_subscription(self, instance, on_data, timeout=60):
          
          manager = WebSocketSubscriptionManager(self, resource='events')
  
          # Represent subscription as a future
          subscription = WebSocketSubscriptionFuture(manager)
  
          wrapped_callback = functools.partial(
              _wrap_callback_parse_event, on_data)
  
          manager.open(wrapped_callback, instance)
  
          # Wait until a reply or exception is received
          subscription.reply(timeout=timeout)
  
          return subscription
docs: Create a new subscription for receiving events of an instance.
  
          This method returns a future, then returns immediately. Stop the
          subscription by canceling the future.
  
          :param str instance: A Yamcs instance name
  
          :param on_data: Function that gets called on each :class:`.Event`.
          :type on_data: Optional[Callable[.Event])
  
          :param timeout: The amount of seconds to wait for the request to
                          complete.
          :type timeout: Optional[float]
  
          :return: Future that can be used to manage the background websocket
                   subscription.
          :rtype: .WebSocketSubscriptionFuture