列表的不兼容类型SupportsIndex上出现mypy错误。\u imul__

Question

我正在用__imul__()的定义对list进行子类化

from __future__ import annotations

from typing import SupportsIndex


class CustomList(list):
    def __imul__(self, n: SupportsIndex) -> CustomList:
        return super().__imul__(n)

Python3.9.2的mypy 0.910会引发一个错误，即参数类型不兼容

customlist.py:8: error: Argument 1 to "__imul__" of "list" has incompatible type "SupportsIndex"; expected "int"

这对我来说毫无意义__imul__()绝对接受SupportsIndex参数。根据docs：

6. The value n is an integer, or an object implementing __index__().

这是mypy中的一个bug吗？有没有办法在不添加本地忽略的情况下解决此错误