Use new-style annotations

Before Python 3.9, you had to import stuff from typing for some annotations:

from typing import List, Dict, Iterator, ContextManager

def foo(things: List[int]) -> ContextManager[Iterator[Dict[str, object]]]:
    ...

After PEP 585 was implemented, already existing classes from the standard library are now generic:

from collections.abc import Iterator
from contextlib import AbstractContextManager

def foo(things: list[int]) -> AbstractContextManager[Iterator[dict[str, object]]]:
    ...

You should be using the new imports instead of the typing ones. It's more convenient to use already available types, but more importantly, these exports from typing are deprecated, and will be removed some day.

If you want to enforce this in your build pipeline, there's a flake8 plugin: flake8-pep585.

The complete list of deprecated symbols can be found as text in PEP 585 or as a Python dictionary on GitHub.