[question] Proper way to implement `ExceptionGroup.derive` method with the existing overloads?

Good afternoon,

I was working to implement some custom exception groups in an application that I work on and have had a really hard time getting the types for the derive function to work correctly. Based on reading the documentation linked below, derive is a required method when overriding an exception group to return an instance of it's own class.

Reference

https://docs.python.org/3/library/exceptions.html#BaseExceptionGroup.derive

Reproduction / Example

To reproduce this error, I'll use the example shows in the BaseExceptionGroup page, but with type hints:

from __future__ import annotations

from collections.abc import Sequence
from typing import TypeVar

_ExceptionT_co = TypeVar("_ExceptionT_co", bound=Exception, covariant=True)
_ExceptionT = TypeVar("_ExceptionT", bound=Exception)


class MyGroup(ExceptionGroup[_ExceptionT_co]):
    def derive(self, excs: Sequence[_ExceptionT]) -> MyGroup[_ExceptionT]:
        return MyGroup(self.message, excs)

Mypy output:

❯ mypy ~/Desktop/example.py
/Users/kkirsche/Desktop/example.py:11: error: Signature of "derive" incompatible with supertype "BaseExceptionGroup"  [override]
/Users/kkirsche/Desktop/example.py:11: note:      Superclass:
/Users/kkirsche/Desktop/example.py:11: note:          @overload
/Users/kkirsche/Desktop/example.py:11: note:          def [_ExceptionT <: Exception] derive(self, Sequence[_ExceptionT], /) -> ExceptionGroup[_ExceptionT]
/Users/kkirsche/Desktop/example.py:11: note:          @overload
/Users/kkirsche/Desktop/example.py:11: note:          def [_BaseExceptionT <: BaseException] derive(self, Sequence[_BaseExceptionT], /) -> BaseExceptionGroup[_BaseExceptionT]
/Users/kkirsche/Desktop/example.py:11: note:      Subclass:
/Users/kkirsche/Desktop/example.py:11: note:          def [_ExceptionT <: Exception] derive(self, excs: Sequence[_ExceptionT]) -> MyGroup[_ExceptionT]
Found 1 error in 1 file (checked 1 source file)

Given that this is working off an exception group rather than a base exception group, I'm unclear on what the proper way to fix this would be and was wondering if the team here was able to provide an example that satisfies mypy / typeshed's overrides for BaseExceptionGroup's derive function.

Thoughts

Would it potentially make sense to add a derive method to ExceptionGroup which returns Self rather than a hardcoded ExceptionGroup? This seems to align with how the documentation describes using this behavior, but I'm not confident I understand fully to submit a pull request with recommended change(s).

Thanks for your time and help, hope you all are having a great day.

首先将 BaseExceptionGroup.derive 的文档与报告中的 MyGroup 示例和 mypy 输出进行比较，然后检查 typeshed 中现有的 BaseExceptionGroup.derive 重载。完成的标准是确定一种受支持的注解或有充分依据的 stub 修改，以解决 override 不匹配问题，并通过复现用例进行验证。