Descriptors shouldn't be considered callable inside class definition

[refi64]

The following is an error in Python but passes mypy's checks:

class X:
    @staticmethod
    def f(): pass
    f()

Error:

Traceback (most recent call last):
  File "cls.py", line 1, in <module>
    class X:
  File "cls.py", line 4, in X
    f()
TypeError: 'staticmethod' object is not callable

Same thing goes for classmethod.

[gvanrossum]

Ugh. Mypy's lack of understanding of class vs. instance attributes strikes again. :-(

[elazarg]

I would expect mypy to mimic the runtime - treat the current block as if it was not inside a class definition, then send the definitions to a "metaclass" (hard coded, in the case to type) to handle. It will also yield a natural extension point for a plugin: implement your home-made "metaclass".

Does that make sense at all? As far as I understand, this isn't how it's done, currently - not even remotely similar.

[gvanrossum]

Would be good to fix but probably complicated.

[gvanrossum]

I think you meant "decorators" in the title, not "descriptors", right? (A decorator uses @ syntax -- a descriptor is something that implements __get__ and (optionally) __set__ and __delete__.

[refi64]

@gvanrossum Well, I meant descriptors because of the staticmethod descriptor.

[gvanrossum]

Ah, got it.

[erictraut]

This doesn't appear to generate a runtime exception with newer versions of Python, so it's no longer a false negative in mypy.

[JelleZijlstra]

The runtime change is from https://bugs.python.org/issue43682 which was included in Python 3.10.

[hauntsaninja]

Closing as won't fix, though if anyone feels inspired to write a PR for 3.9 feel free to