issue with SUBSCRIBE and pipes

[thomasst]

Sample code:

redis = Redis()

# If I enable this line it works (i.e. executing any redis command before executing the pipe). This shouldn't be required though.
#redis.exists('z')

pipe = redis.pipeline()
pipe.subscribe('z')
print 'exec', pipe.execute()

for msg in pipe.listen():
    print msg


Output:

Traceback (most recent call last):
  File "sub.py", line 14, in 
    print 'exec', pipe.execute()
  File "/home/tom/lib/redis/client.py", line 1151, in execute
    return execute(stack)
  File "/home/tom/lib/redis/client.py", line 1113, in _execute_transaction
    self.connection.send(all_cmds, self)
  File "/home/tom/lib/redis/client.py", line 81, in send
    self.connect(redis_instance)
  File "/home/tom/lib/redis/client.py", line 66, in connect
    redis_instance._setup_connection()
  File "/home/tom/lib/redis/client.py", line 395, in _setup_connection
    self.execute_command('SELECT', self.connection.db)
  File "/home/tom/lib/redis/client.py", line 302, in execute_command
    **options
  File "/home/tom/lib/redis/client.py", line 1100, in _execute_command
    command_name, command, **options)
  File "/home/tom/lib/redis/client.py", line 278, in _execute_command
    raise RedisError("Cannot issue commands other than SUBSCRIBE and "
redis.exceptions.RedisError: Cannot issue commands other than SUBSCRIBE and UNSUBSCRIBE while channels are open

[thomasst]

Also, the following does not work:

redis.exists('z')

pipe = redis.pipeline()

pipe.zrange('z', 0, -1)
pipe.subscribe('z')

msgs, subs = pipe.execute()
print msgs

redis.unsubscribe()

print 'unsubscribed'

redis.exists('z')

pipe = redis.pipeline()

pipe.zrange('z', 0, -1)
pipe.subscribe('z')

msgs, subs = pipe.execute() # fails here
print msgs

redis.unsubscribe()

Traceback (most recent call last):
  File "sub.py", line 36, in 
    msgs, subs = pipe.execute()
  File "/home/tom/lib/redis/client.py", line 1151, in execute
    return execute(stack)
  File "/home/tom/lib/redis/client.py", line 1120, in _execute_transaction
    raise ResponseError("Wrong number of response items from "
redis.exceptions.ResponseError: Wrong number of response items from pipline execution

BTW: "pipline" has a typo.

[andymccurdy]

So I took another look at this during PyCon. I'm tempted to just make calling (P)SUBSCRIBE, (P)UNSUBSCRIBE and LISTEN impossible from pipelines. Can anyone give me a use case why they'd want to subscribe or listen to channels from a pipeline?

[andymccurdy]

redis-py 2.4 removes the ability for pipelines to subscribe to channels.