List instead of set for SMEMBERS in 5.1

[jules-ch]

Version: What redis-py and what redis version is the issue happening on?

Platform: What platform / version? Python 3.11 Ubuntu 24.04

Description: smembers is returning a list instead of a set in redis-py 5.1.0 which is an unintended breaking change.
Before:

>>> from redis import Redis
>>> pool = Redis.from_url("redis://", decode_responses=True)
>>> pool.sadd("users", "user1")
0
>>> pool.smembers("users")
{'user1'}

AFter

>>> from redis import Redis
>>> pool = Redis.from_url("redis://", decode_responses=True)
>>> pool.sadd("users", "user1")
0
>>> pool.smembers("users")
['user1']

[jules-ch]

Seems to be done in #3324 (comment)

Can you add this in the list of the breaking changes in 5.1, it's not documented.
Also stubs from types-redis need to be changed`

[dmaier-redislabs]

Hi Jules,

we had a note under bug fixes. I copied it over to the breaking changes section to make it more visible. Which RESP version are you using?

@vladvildanov I think we need to take a second look at this change.

Regards,
David

[jules-ch]

I did not specified RESP protocol version somewhere, is it tied to Redis server version ?

[vladvildanov]

@jules-ch Thanks for reaching us! Changes in those PR should only affect RESP3 users, I'll have a look on it

[dmaier-redislabs]

Hi @jules-ch ,

we did take another look and this impacts RESP2 and RESP3 with and without hiredis-py for response parsing. This was introduced as part of a bug fix in the context of dealing with RESP3 sets (message format).

So we decided that the original fix should never have impacted the result of the set (data structure) commands. We will release a patch version of 5.1 that reverts this breaking change for those commands. The original fix will still have an intended impact on some commands (e.g., the COMMAND command), but we will ensure that all the S* commands (e.g., SADD) will behave semantically correct again by returning a set instead of a list. We apologize for the inconvenience that this has caused.

Regards,
David

[jules-ch]

@dmaier-redislabs Alright makes sense, thanks for the quick fix, I'll wait before updating.

Closing this issue.

[dmaier-redislabs]

Reopening it until we released 5.1.1