[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.

Bắt đầu bằng cách so sánh tài liệu của BaseExceptionGroup.derive với ví dụ MyGroup được báo cáo và đầu ra của mypy, sau đó kiểm tra các overload hiện có trong typeshed cho BaseExceptionGroup.derive. Được xem là hoàn tất khi xác định được một annotation được hỗ trợ hoặc một thay đổi stub có cơ sở để giải quyết lỗi không khớp override, kèm theo việc xác thực với bản tái hiện.