add types.MethodType.__get__ on py313+

[jorenham]

runtime behavior (3.13):

>>> class A:
...     def f(self): ...
...     
>>> f = A().f
>>> f.__get__(object()) is f
True
>>> f.__get__(object(), object) is f
True
>>> f.__get__(object(), None) is f
True
>>> f.__get__(object, None) is f
True
>>> f.__get__(object) is f
True

related to https://discuss.python.org/t/when-should-we-assume-callable-types-are-method-descriptors/92938

[srittau]

Could you remove the extra newlines that were probably inserted by your autoformatter?

[jorenham]

Could you remove the extra newlines that were probably inserted by your autoformatter?

ah yes sorry about that; rookie mistake

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

archinstall (https://github.com/archlinux/archinstall)
- ./archinstall/tui/curses_menu.py:710: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
- https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
- Please report a bug at https://github.com/python/mypy/issues
- version: 1.15.0
- ./archinstall/tui/curses_menu.py:710: : note: use --pdb to drop into pdb
- Traceback (most recent call last):
-   File "mypy/checkexpr.py", line 5903, in accept
-   File "mypy/nodes.py", line 1889, in accept
-   File "mypy/checkexpr.py", line 3284, in visit_member_expr
-   File "mypy/checkexpr.py", line 3309, in analyze_ordinary_member_access
-   File "mypy/checkmember.py", line 207, in analyze_member_access
-   File "mypy/checkmember.py", line 226, in _analyze_member_access
-   File "mypy/checkmember.py", line 344, in analyze_instance_member_access
-   File "mypy/meet.py", line 96, in meet_types
-   File "mypy/subtypes.py", line 223, in is_proper_subtype
-   File "mypy/subtypes.py", line 351, in _is_subtype
-   File "mypy/types.py", line 1469, in accept
-   File "mypy/subtypes.py", line 581, in visit_instance
-   File "mypy/subtypes.py", line 2095, in infer_class_variances
-   File "mypy/subtypes.py", line 2057, in infer_variance
-   File "mypy/subtypes.py", line 186, in is_subtype
-   File "mypy/subtypes.py", line 351, in _is_subtype
-   File "mypy/types.py", line 3033, in accept
-   File "mypy/subtypes.py", line 1079, in visit_partial_type
- RuntimeError: Partial type "<partial list[?]>" cannot be checked with "issubtype()"

[jorenham]

primer crash location: https://github.com/archlinux/archinstall/blob/47e6d82ee564ba1192a63d5f9ea89270a7cdf32e/archinstall/tui/curses_menu.py#L710

caused by archlinux/archinstall@bd36c0c

[JelleZijlstra]

Interestingly that crash also went away with #14198, which suggests it's a case of nondeterminism in mypy.

[srittau]

Primer passed previously.