'Sleep between retry attempts.
This method will respect a server\'s ``Retry-After`` response header
and sleep the duration of the time requested. If that is not present, it
will use an exponential backoff. By default, the backoff factor is 0 and
this method will return immediately.'

def sleep(self, response=None):

    if response:
        slept = self.sleep_for_retry(response)
        if slept:
            return
    self._sleep_backoff()
