delete() take in a list of keys

[woozyking]

The use case came up when I tried to do this:

# conn is a valid StrictRedis instance
keys = conn.keys('namespace:*')  # this returns a list
conn.delete(keys)  # does not delete all the keys in the list

conn.delete(*keys)  # raises ResponseError: wrong number of arguments for 'del' command

# edit: conn.delete(*keys) works when the list is not empty

Can we make it a bit neater to allow delete to just accept a list or a set of strings (keys) to do the necessary check to be passed to execute_command('DEL', ...)?

[andymccurdy]

The current behavior lets you do:

conn.delete('my-key')
conn.delete('my-key-1', 'my-key-2')
conn.delete(*list_of_keys)

That seems pretty Pythonic to me.

[woozyking]

It is pythonic, but when you do conn.delete(*list_of_keys), list_of_keys must not be empty or it'll raise ResponseError: wrong number of arguments for 'del' command.

I'm just proposing for a slightly more convenient interface for users who can just pass in a list or a set of strings to be deleted.

[AndrewGuenther]

I think a simple check in the delete command would suffice. No? If it simply bailed out when *list_of_keys is empty?

[andymccurdy]

So there's two issues here:

1. The signature to the delete() command. I prefer the *args version because it makes it trivial for the common case of r.delete('my-key') and because other commands that accept 1 or more arguments use the *args pattern already. I don't think having a * or not is really worth arguing over.
2. What to do when 0 keys are passed to delete(). This one is harder. All commands must either call execute_command or raise an error. A command that does neither of these will cause problems with pipelines. Imagine the following scenario:

r = redis.StrictRedis()
pipe = r.pipeline()
pipe.set('key-1', 'value-1')
pipe.delete(*r.keys('keys-to-delete:*'))
pipe.rpush('key-2', 'value'-2')
pipe.execute()

The pipeline's execute() returns a list of 3 responses, one for the SET, one for the DELETE, and one for the RPUSH. If execute_command doesn't get invoked for the DELETE command the pipeline's execute() would only contain two responses.

I don't see a way to make this work.

[woozyking]

I see the point. If this is by design, and especially due to how it should comply with pipeline functionality, then I agree that users should make the emptiness check at the application level.

Do you think this is worth mentioning in the documentation though? Personally I think this is still an odd convention for people who don't know the actual details regarding why no implicit check is done within delete for *args; and/or, add to the description of the exception raised to something like ResponseError: wrong number of arguments for 'del' command. Arguments must not be empty or something that more concisely and clearly reflect the behavior of the method.

[brejoc]

I ran into this issue last week in the context of the redis returner in SaltStack. It took me some time to dig out the true source for this error, because I was not aware, that Salt tried to pass an empty list. A slightly modified error message would have been a huge benefit.

[github-actions]

This issue is marked stale. It will be closed in 30 days if it is not updated.