code: def completed_stage(self, stage):
          
          check_path = checkpoint_filepath(stage, self.manager)
          return os.path.exists(check_path)
docs: Determine whether the pipeline's completed the stage indicated.
  
          :param pypiper.Stage stage: Stage to check for completion status.
          :return bool: Whether this pipeline's completed the indicated stage.
          :raises UnknownStageException: If the stage name given is undefined
              for the pipeline, a ValueError arises.