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