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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def retry(self, retry_message=''):
 """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. """

    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