Implement B037 check for yielding or returning values in __init__()

[r-downing]

Implement check for return <value>, yield, yield <value>, or yield from <value> in class __init__() method. No values should be returned or yielded, only bare returns are ok.

These would be runtime errors, if and when these statements are reached.

This does trigger on return None which is equivalent to return, but kind of confusing and pointless to write in a function that shouldn't return anything.

[cooperlees]

LGTM - But I think I would like if we allowed return None unless it's difficult that I'm not seeing ...

I'm a big explicit is better than implicit person ...

[cooperlees]

I can see people disliking this due to

Explicit is better than implicit

In the Zen of Python.

Can we just check if a None is being explicitly returned and not error in that case since we allow return ...

[r-downing]

Yeah it's easy enough to do if you prefer, but my argument against allowing return None is that, while return is functionally equivalent to return None in python, the latter should only be used in cases where you might return something (like a C function that returns either a valid pointer or NULL). Whereas just bare return is ok, when used as a early exit point from a function (like a C void function).

some quick examples:

def get_thing() -> Thing | None:
    """return a thing if possible"""
    for thing in things:
        if condition:
            return thing
    return None  # this line could be omitted, but functions that have a non-empty return
                 # in some case should have non-empty return in all cases (pylint would 
                 # complain about this for example)

vs

class Example:
    def __init__(self, size, do_extra_stuff = False):
        self.x = ...

        if not do_extra_stuff:
            return  # early exit. Could do `return None` but that implies
                    # that we might return something somewhere else?

        # do some more stuff

let me know what you think, thanks!

[JelleZijlstra]

I agree that it's better to lint against return None.

[cooperlees]

Since this is __init__ only, I can live with it. I'll have code to 'fix' cause of it.

[JelleZijlstra]

Might be cleaner to put this inside the BugBearVisitor

[r-downing]

Done, LMK if that looks better

[r-downing]

Waiting on anything else here?

[cooperlees]

Since this is __init__ only, I can live with it. I'll have code to 'fix' cause of it.