false positive too-many-ancestors if class inherits MutableMapping

[kiefermat]

Steps to reproduce

Given a file a.py:

# pylint: disable=missing-docstring

from typing import Iterator, MutableMapping, Optional


class PylintTestMap(MutableMapping[str, str]):
    config: MutableMapping[str, str] = dict()

    def __getitem__(self, item: str) -> Optional[str]:
        return self.config.get(item)

    def __len__(self) -> int:
        return len(self.config)

    def __iter__(self) -> Iterator[str]:
        return iter(self.config)

    def __setitem__(self, key: str, value: str) -> None:
        self.config[key] = value

    def __delitem__(self, key: str) -> None:
        del self.config[key]

Current behavior

Result of pylint a.py:

************* Module a
a.py:7:0: R0901: Too many ancestors (8/7) (too-many-ancestors)

------------------------------------------------------------------
Your code has been rated at 9.23/10 (previous run: 9.23/10, +0.00)

Expected behavior

No warning about ancestors

pylint --version output

Result of pylint --version output:

pylint 2.7.2
astroid 2.5.1
Python 3.9.1

This behaviour has been introduced with pylint 2.7.2. pylint 2.7.1 does not show this warning.

[Pierre-Sassoulas]

I think this is due to pylint-dev/astroid#916. Ie Mutable set has a long inheritance tree already "V => MutableSet => Set => Collection => Sized => Iterable => Container => Generic => object". We should probably start counting at the first non builtin type for too-many-ancestor.

[winstxnhdw]

Hey, I am getting this issue but with TypedDict from typing_extensions..

[Pierre-Sassoulas]

I think it's because it's a non-builtin that we do not filter. As typing_extension is so widespread, maybe we could add it to the list here https://github.com/pylint-dev/pylint/pull/4416/files#diff-1fc8e30254a5d218a85ae17846638d3c9393d32819beec7d59d3fdbdea073c6aR178. Would you mind opening a merge request ?

[winstxnhdw]

Happily #9167