PLE0237 false positive

[henryiii]

Currently, PLE0237 will report "Attribute other is not defined in class's __slots__" on a class like this:

class A:
    __slots__ = ("pub",)

    def __init__(self) -> None:
        self.other = "hi"

Which is correct. But it also reports the same error on the following correct class:

class B:
    __slots__ = ("pub", "__dict__")

    def __init__(self) -> None:
        self.other = "hi"

This is incorrect; since the class has a __dict__ in it's __slots__, it has a dict to put other in. This is described in https://docs.python.org/3/reference/datamodel.html#slots (both __dict__ and __weakref__ can be declared in __slots__), and is an important technique for wrapper classes, where the wrapped object is declared in slots, so that the __dict__ has everything except the wrapped object.

Incorrect check result seen in scikit-hep/boost-histogram#914.

• Command ruff check --select=ALL --isolated tmp.py
• Ruff version: ruff 0.3.1

[charliermarsh]

Thanks!

[charliermarsh]

So is it correct to effectively turn off this check when __dict__ is present?

[henryiii]

Basically. The condition is actually if a class has a __dict__, not if it has __slots__. Classes without __slots__ (anywhere in the inheritance chain) automatically get a __dict__. Classes with __slots__ (including in every parent) only get a dict if it's added manually in __slots__.

I assume you couldn't handle complex cases, but in the most common simple case of of a __slots__ having a string "__dict__", I assume you could treat that like a dict class?