code: def handle(client_message, handle_event_partition_lost=None, to_object=None):
      
      message_type = client_message.get_message_type()
      if message_type == EVENT_PARTITIONLOST and handle_event_partition_lost is not None:
          partition_id = client_message.read_int()
          lost_backup_count = client_message.read_int()
          source = None
          if not client_message.read_bool():
              source = AddressCodec.decode(client_message, to_object)
          handle_event_partition_lost(partition_id=partition_id, lost_backup_count=lost_backup_count, source=source)
docs: Event handler