Redis (Python client) support for numsub?

Redis (Python client) support for numsub?

I am using redis-py to talk with my Redis server. I'm interested in using
the numsub function that was outlined in the Redis documentation
(http://redis.io/commands/pubsub), but I can't figure out if this is
supported in redis-py.
This is what I have code-wise:
import redis
r = redis.Redis()
ps = r.pubsub()
ps.subscribe('mychannel')
I have tried:
print ps.numsub('mychannel')
print r.numsub('mychannel')
Can anyone help? Thanks!