code: def notification_factory(code, subcode):
      
      notification = BGPNotification(code, subcode)
      if not notification.reason:
          raise ValueError('Invalid code/sub-code.')
  
      return notification
docs: Returns a `Notification` message corresponding to given codes.
  
      Parameters:
      - `code`: (int) BGP error code
      - `subcode`: (int) BGP error sub-code