def _pull(self):
        """
        A generator that calls C{resumeProducing} on the underlying producer
        forever.

        If C{resumeProducing} throws an exception, the producer is
        unregistered, which should result in streaming stopping.
        """
        while True:
            try:
                self._producer.resumeProducing()
            except:
                log.err(None, "%s failed, producing will be stopped:" %
                        (safe_str(self._producer),))
                try:
                    self._consumer.unregisterProducer()
                    # The consumer should now call stopStreaming() on us,
                    # thus stopping the streaming.
                except:
                    # Since the consumer blew up, we may not have had
                    # stopStreaming() called, so we just stop on our own:
                    log.err(None, "%s failed to unregister producer:" %
                            (safe_str(self._consumer),))
                    self._finished = True
                    return
            yield None

        A generator that calls C{resumeProducing} on the underlying producer
        forever.

        If C{resumeProducing} throws an exception, the producer is
        unregistered, which should result in streaming stopping.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/_producer_helpers.py