while expression feature proposal

[Dan Loewenherz]

It seems the topic of this thread has changed drastically from the original message.

1) "while EXPR as VAR" in no way says that EXPR must be a boolean value. In fact, a use case I've run into commonly in web development is popping from a redis set. E.g.

    client = StrictRedis()
    while True:
        profile_id = client.spop("profile_ids")
        if not profile_id:
            break
        print profile_id

In this case, profile_id is "None" when the loop breaks. It would be much more straightforward (and more Pythonic, IMO), to write:

    client = StrictRedis()
    while client.spop("profile_ids") as profile_id:
        print profile_id

2) Although not originally intended, I kind of like the "if" statement change proposed later in this thread. It certainly makes sense, since both while and if are "conditional" statements that are commonly followed by an assignment (or vice versa).

3) I don't think the use case I brought up is solved nicely by wrapping a function / lambda in a generator and using a for loop. E.g.

    def helper(f):
        value = f()
        if value:
            yield value

    for profile_id in helper(lambda: client.spop("profile_ids")):
        print profile_id

This works too, I guess

    def helper(f, *args, **kwargs):
        value = f(*args, **kwargs)
        if value:
            yield value

    for profile_id in helper(client.spop, "profile_ids"):
        print profile_id

Either way, it adds too much mental overhead. Every developer on a project has to now insert x lines of code before a for loop or import a helper method from some module, and do this every time this pattern reappears. It's not something I would want to do in one of my projects, since it makes things harder to understand. So all in all, it's a net negative from just doing things the canonical way (with the while / assignment pattern).

Dan