"Union" is not replaced with "|" in user-defined type hints

[simon-liebehenschel]

Sample code:

from typing import Union

FooBar = Union[str, int]

Current result:

No changes

Expected result

FooBar = int | str

---

pre-commit config:

  - repo: https://github.com/asottile/pyupgrade
    rev: v2.32.1
    hooks:
      - id: pyupgrade
        args: [--py310-plus]

---

I've tried to search over open and closed issues, but I found nothing. If it is an expected behavior, then it will be nice to document this.

[asottile]

this was intentionally omitted because type checkers did not support it

[sjdemartini]

Should the behavior in pyupgrade be changed now that mypy supports the PEP604 syntax python/mypy#9880, so that user-defined type-hints with Union aren't ignored?

[asottile]

perhaps! feel free to send a tested patch