`get_original_bases` does not return what `cls.__orig_bases__` returns

Bug report

Bug description:

The types documentation states for the types.get_original_bases function:

For classes that have an __orig_bases__ attribute, this function returns the value of cls.__orig_bases__. For classes without the __orig_bases__ attribute, cls.__bases__ is returned.

I need the functionality of cls.__orig_bases__, but need to use types.get_original_bases to make the type checker happy.

A short MRE:

from types import get_original_bases
from typing import Generic, TypeVar

T = TypeVar("T")


class One(Generic[T]):
    pass


class Two(One[int]):
    pass


class Three(Two):
    pass


assert get_original_bases(One) == One.__orig_bases__
assert get_original_bases(Two) == Two.__orig_bases__
assert get_original_bases(Three) == Three.__orig_bases__

# Traceback (most recent call last):
#   File "c:\<cut>\test.py", line 34, in <module>
#     assert get_original_bases(Three) == Three.__orig_bases__
#            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# AssertionError

This is a easy solve, I would be happy to add a PR. Change here:

    try:
-       return cls.__dict__.get("__orig_bases__", cls.__bases__)
+       return getattr(cls, "__orig_bases__", cls.__bases__)
    except AttributeError:
        raise TypeError(
            f"Expected an instance of type, not {type(cls).__name__!r}"
        ) from None

To show this works:

from typing import Generic, TypeVar

T = TypeVar("T")


class One(Generic[T]):
    pass


class Two(One[int]):
    pass


class Three(Two):
    pass


def better_get_original_bases(cls):
    try:
        return getattr(cls, "__orig_bases__", cls.__bases__)
    except AttributeError:
        raise TypeError(
            f"Expected an instance of type, not {type(cls).__name__!r}"
        ) from None


assert better_get_original_bases(One) == One.__orig_bases__
assert better_get_original_bases(Two) == Two.__orig_bases__
assert better_get_original_bases(Three) == Three.__orig_bases__

# <No output>

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Linked PRs

• gh-156917

Bắt đầu trong Lib/types.py tại get_original_bases và tái hiện ví dụ về tính kế thừa trong issue, bao gồm cả trường hợp lớp Three. Công việc được xem là hoàn tất khi hàm khớp với hành vi original-bases được tài liệu hóa và phạm vi kiểm thử hồi quy xác minh trường hợp thuộc tính được kế thừa; hãy xem lại PR được liên kết gh-156917 trước khi bắt đầu.