Incorrect deduplication of Enum values in Union[Literal[1], Literal[SomeEnum.one]]

[adriangb]

This was fixed on 3.9 (by #23294 or followups). Here's a test / example:

from enum import Enum
from typing import Literal, Union, get_args


class MyEnum(int, Enum):
    foo = 1

tp = Union[Literal[MyEnum.foo], Literal[1]]
assert len(get_args(tp)) == 2, get_args(tp)

tp = Union[Literal[1], Literal[MyEnum.foo]]
assert len(get_args(tp)) == 2, get_args(tp)

These assertions fail on 3.8 since Union deduplicates both Literals into the same thing. The reason you need Literal here is because enum values are values not types so they can only appear in a Union if they're also within a Literal.

As per #23294 (comment) maybe the answer here is to not do anything. And in fact I looked into back porting and it was too big of a change to be called a back port. But I didn't see this specific issue w/ Enum and Union reported, so I at least wanted to report it and confirm that it is a bug.

Linked PRs

• gh-103592: Add tests of Literal with Enum and Union of Literals #103706
• [3.11] gh-103592: Add tests of Literal with Enum and Union of Literals (GH-103706) #103720

[JelleZijlstra]

3.8 is in security fix-only mode, so it's too late to fix this.

[adriangb]

Makes sense. I'll just close the issue then.

[adriangb]

Do you think we can change https://github.com/python/typing_extensions/blob/501a00e4701185ec93220155a0caa3da71d327e8/src/typing_extensions.py#L264-L268 to use the typing-extensions implementation for 3.8 as well?

[JelleZijlstra]

Yes, that makes sense to do.

[sobolevn]

test_typing.py police is here 🚨

This is not tested right now, in fact, Literal with enum is never tested at all.
Moreover, we don't have a single Union[Literal, Literal, ...] test as well.

Thanks a lot @adriangb for raising this.
PR with the fix is ready :)