bpo-46571: improve typing.no_type_check to skip foreign objects

[sobolevn]

There are several changes:

1. We now don't explicitly check for any base / sub types, because new name check covers it
2. I've also checked that no_type_check do not modify foreign functions. It was the same as with types
3. I've also covered except TypeError in no_type_check with a simple test case, it was not covered at all
4. I also felt like adding lambda test is a good idea: because lambda is a bit of both in class bodies: a function and an assignment

Are there any other cases we want to cover?

https://bugs.python.org/issue46571

[AlexWaygood]

Here's a slightly evil corner case that this patch doesn't account for:

If I have a module typing_test.py, like so:

# typing_test.py
class A:
    class AA:
        foo: int

Then, observe the following behaviour (with your patch applied):

>>> from typing import get_type_hints, no_type_check
>>> import typing_test
>>> get_type_hints(typing_test.A.AA)
{'foo': <class 'int'>}
>>> @no_type_check
... class A:
...     AA = typing_test.A.AA
... 
...     
>>> get_type_hints(typing_test.A.AA)
{}

We might be able to get around this by looking at the __module__ attribute.

[sobolevn]

@AlexWaygood good one! Very evil!

I've addressed this.

@JelleZijlstra I agree that we should also fix classmethod / staticmethod problem. Because we declare to support all methods, not just instance methods.

The problem is that types.MethodType does not support attribute assignment:

>>> class Some:
...     @staticmethod
...     def st(x: int) -> int: ...
...     @classmethod
...     def cl(cls, y: int) -> int: ...

>>> Some.st.__no_type_check__ = True

>>> Some.cl.__no_type_check__ = True
AttributeError: 'method' object has no attribute '__no_type_check__'

Ideas?

Moreover, do we need some special @property support?

[AlexWaygood]

@AlexWaygood good one! Very evil!

I've addressed this.

Doesn't look like you've pushed anything -- did you mean to? :)

[sobolevn]

Doesn't look like you've pushed anything -- did you mean to? :)

Not yet, I am still fighting classmethod 🙂

[sobolevn]

Probably

if isinstance(obj, types.MethodType):
                obj.__func__.__no_type_check__ = True

is the way to go 🤔

Will write some more tests to be sure.

[JelleZijlstra]

Looks good.

Do you think this should be backported? I'm leaning no as it's a behavior change and nobody directly complained about the old behavior (looks like you found it while reviewing typing test coverage).

[gvanrossum]

Agreed, a backport doesn't seem asked for.