`Generator` type annotation wrongly shortened

[david-zwicker]

pyupgrade turns the following code

def f() -> Generator[float, None, None]:
    ...

into

def f() -> Generator[float]:
    ...

which is wrong according to mypy. I believe pyupgrade should keep the three-argument version.

[asottile]

you're on an old mypy

[david-zwicker]

I'm on mypy 1.11.1 (compiled: yes), which I believe is the latest one.

[asottile]

show your output and full code?

[david-zwicker]

I cannot fully isolate the problem, but it appears in the code base of py-pde. I'll try to come up with a minimal example and post it here!

[asottile]

please start with that next time instead of wasting my time!

[e-gebes]

I have the same or a similar issue. I ran pyupgrade --py310-plus myfile.py on the following code

from __future__ import annotations

from collections.abc import Generator

def generator() -> Generator[int, None, None]:
    yield 1

and it gets shortened to:

from __future__ import annotations

from collections.abc import Generator

def generator() -> Generator[int]:
    yield 1

My version of pyupgrade is 3.17.0

Without the from __future__ import annotations line the Generator type hint is not shortened.

I think

• the shortening should not depend on that future import
• the shortening should be done for Python 3.13 code only, and not when run with the --py310-plus flag. The CPython docs mention the possibility for shortening only since Python 3.13: link. The current mypy stable (1.11.2) docs do not mention the shortening: link, also not the typing documentation (as of now).

[asottile]

you're wrong. mypy accepts it just fine with the import just like all other improvements.

where are you seeing otherwise?

[e-gebes]

it's irrelevant if a code optimization works with one specific tool read the CPython doc!

it's legitimate to write Python 3.10 code, it's legitimate to write 3.10 code with the annotations import, and it's legitimate to write the type hints in the same 3.10-way

when I run pyupgrade --py310-plus apparently the "3.10 type hints" are upgraded to 3.13 type hints (!), which is surprising behavior - it'd be better to change that

at least the behavior is somehow documented: https://github.com/asottile/pyupgrade?tab=readme-ov-file#pep-696-typevar-defaults and there's remedy with --keep-runtime-typing in this case

[asottile]

read the pyupgrade doc!

you still haven't demonstrated any breakage so I'm assuming you're just a troll