code: def retry(self, retry_message=''):
      
      if not self.async:
        raise UnexpectedPipelineError(
            'May only call retry() method for asynchronous pipelines.')
      if self.try_cancel():
        self._context.transition_retry(self._pipeline_key, retry_message)
        return True
      else:
        return False
docs: Forces a currently running asynchronous pipeline to retry.
  
      Note this may not be called by synchronous or generator pipelines. Those
      must instead raise the 'Retry' exception during execution.
  
      Args:
        retry_message: Optional message explaining why the retry happened.
  
      Returns:
        True if the Pipeline should be retried, False if it cannot be cancelled
        mid-flight for some reason.