code: def format(self, record):
          
          message = super(ContainerEngineHandler, self).format(record)
          return format_stackdriver_json(record, message)
docs: Format the message into JSON expected by fluentd.
  
          :type record: :class:`~logging.LogRecord`
          :param record: the log record
  
          :rtype: str
          :returns: A JSON string formatted for GKE fluentd.