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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 completed_stage(self, stage):
 """ 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. """

        check_path = checkpoint_filepath(stage, self.manager)
        return os.path.exists(check_path)