code: def _retry_fetch(self, after=None):
          
  
          # Have we been told to stop or shutdown?  Then don't actually retry.
          if self._stopping or self._shuttingdown or self._start_d is None:
              # Stopping, or stopped already? No more fetching.
              return
          if self._retry_call is None:
              if after is None:
                  after = self.retry_delay
                  self.retry_delay = min(self.retry_delay * REQUEST_RETRY_FACTOR,
                                         self.retry_max_delay)
  
              self._fetch_attempt_count += 1
              self._retry_call = self.client.reactor.callLater(
                  after, self._do_fetch)
docs: Schedule a delayed :meth:`_do_fetch` call after a failure
  
          :param float after:
              The delay in seconds after which to do the retried fetch. If
              `None`, our internal :attr:`retry_delay` is used, and adjusted by
              :const:`REQUEST_RETRY_FACTOR`.