I have two consumers for a topic that only has one partition. When the idle consumer is running it prints out a constant stream of:
"_poll called with a non-zero timeout and sleep=False -- but there was nothing to do. This can cause high CPU usage during idle."

This is similar to issue #494 that had been fixed but it seems that commit b8c2097 broke it again. There is no way to pass the sleep=True parameter to the client object when calling the poll method of the KafkaConsumer object (in group.py). I tried changing line 465 of group.py to:
self._client.poll(timeout_ms, sleep=True)

and then everything worked correctly again. I don't see the reason for commit b8c2097 so I don't know if this would break anything else.