from __future__ import annotations ignored

[clo-vis]

Bug description

from __future__ import annotations
from csv import DictWriter
from typing import IO


def f_is_for_fun(file: IO[str]) -> DictWriter[str]:
    return DictWriter(file, ["id", "name"])

Reference #6519

Command used

pylint playground.py

Pylint output

************* Module playground
…
playground.py:6:35: E1136: Value 'DictWriter' is unsubscriptable (unsubscriptable-object)

Expected behavior

No error, as the python interpreter doesn't complain, nor does mypy, and #3320 is closed.

Pylint version

pylint 2.13.8
astroid 2.11.4
Python 3.9.12 (tags/v3.9.12:b28265d, Mar 23 2022, 23:52:46) [MSC v.1929 64 bit (AMD64)]

[cdce8p]

Sorry for dismissing your first issue that early. At the moment, pylint checks if the classname is in a predefined set of allowed subscriptable names since we don't check the pyi files. It only contains the classes explicitly mentioned in PEP 585. Thus DictWriter but also others like Popen #4369 or Queue do emit a warning.
https://github.com/PyCQA/pylint/blob/7e1b9ae5f974d03e8a584631f85002127cb9405e/pylint/checkers/utils.py#L1402

Since we can't know if a class is subscriptable in typeshed, it might be time to remove the PEP 585 name check.

[hmc-cs-mdrissi]

More broadly generic type may not be from typeshed but from other .pyi files which may be defined in arbitrary locations (well depends on type checker's search paths for stubs). As an example mypy supports MYPY_PATH allowing defining other places for type stubs separate from python path. pyright similarly has it's own setting for possible places .pyi files can be placed. I use custom type stubs for 3rd party libraries that lack type hints.

[cdce8p]

@hmc-cs-mdrissi You're right of course. Pylint isn't a type checker and thus doesn't use .pyi files at all.
Probably the best way forward for us is thus to ignore all unsubscriptable-object errors in string annotations and with from __future__ import annotations. Those don't result in runtime errors and a type checker would catch them anyway.

I've opened #6536 to make that change.