code: def error_message(self):
      
      error = google_v2_operations.get_error(self._op)
      if error:
        job_id = self.get_field('job-id')
        task_id = self.get_field('task-id')
        task_str = job_id if task_id is None else '{} (task: {})'.format(
            job_id, task_id)
  
        return 'Error in {} - code {}: {}'.format(task_str, error['code'],
                                                  error['message'])
  
      return ''
docs: Returns an error message if the operation failed for any reason.
  
      Failure as defined here means ended for any reason other than 'success'.
      This means that a successful cancelation will also return an error message.
  
      Returns:
        string, string will be empty if job did not error.