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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:
 async def _delay(self):
 """Check for a 'retry-after' header to set timeout, otherwise use configured timeout. """

        if self._response is None:
            await asyncio.sleep(0)
        if self._response.headers.get('retry-after'):
            await asyncio.sleep(int(self._response.headers['retry-after']))
        else:
            await asyncio.sleep(self._timeout)