Add an option to avoid releasing PubSub connection

[flupke]

I ran into a problem trying to reuse a single PubSub object for many channels:

client = Redis()
pubsub = client.pubsub()
pubsub.subscribe('foo')
# [...]
pubsub.unsubscribe('foo')
pubsub.subscribe('bar')
for message in pubsub.listen():
    pass

The last listen() fails, because the PubSub connection is None at this time:

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/gevent/greenlet.py", line 328, in run
    result = self._run(*self.args, **self.kwargs)
# [...]
  File "/home/flupke/src/ext/redis-py/redis/client.py", line 1496, in listen
    r = self.parse_response()
  File "/home/flupke/src/ext/redis-py/redis/client.py", line 1440, in parse_response
    response = self.connection.read_response()
AttributeError: 'NoneType' object has no attribute 'read_response'

This is because I wasn't parsing responses, and PubSub recycles the connection when it catches a response indicating there are no more channels subscriptions. The fix is to parse responses after each pub/sub call:

client = Redis()
pubsub = client.pubsub()
pubsub.subscribe('foo')
pubsub.parse_response()
# [...]
pubsub.unsubscribe('foo')
pubsub.parse_response()
pubsub.subscribe('bar')
pubsub.parse_response()
for message in pubsub.listen():
    pass

This is a bit cumbersome, but the real problem is that an unnecessary Redis disconnect/connect cycle is made. The patch adds a release_connection option to StrictRedis.pubsub() and PubSub's constructor to avoid this behavior.

[travisbot]

This pull request passes (merged 2ef7730 into 5209844).

[leetrout]

Is there a reason this hasn't been merged?

I've hit the same issue...

[andymccurdy]

Hi. Many apologies on taking so long to cleanup Publish/Subscribe in redis-py. I've recently had some time to make some big improvements and I'd love to get your feedback.

I believe that the changes I've made solve this issue.

You can review the changes in the pubsub branch here: https://github.com/andymccurdy/redis-py/tree/pubsub

I've written a section in the README docs about PubSub that covers most (hopefully all!) use cases. You can find it here: https://github.com/andymccurdy/redis-py/blob/pubsub/README.rst#publish--subscribe

My current plan is to merge the pubsub branch into master and roll a new release of redis-py by the end of the week. Again, I'd love any feedback.

[andymccurdy]

redis-py 2.10 is out with the new PubSub system.