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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 _shutdownBatchSystem(self):
 """ Shuts down current batch system if it has been created. """

        assert self._batchSystem is not None

        startTime = time.time()
        logger.debug('Shutting down batch system ...')
        self._batchSystem.shutdown()
        logger.debug('... finished shutting down the batch system in %s seconds.'
                     % (time.time() - startTime))