csv.DictReader and DictWriter not subscriptable at runtime #92391

Feature or enhancement

Add PEP 585 style __class_getitem__ to csv.DictReader and csv.DictWriter.

Pitch

With PEP 585 most generic stdlib types are now subscriptable at runtime. Both DictReader and DictWriter are generic in typeshed but don't yet implement __class_getitem__.

from csv import DictWriter
from typing import IO

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

Previous discussion

• bpo-39481: PEP 585 for a variety of modules #19423
• https://mypy.readthedocs.io/en/stable/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime