update ellipsis type

[DetachHead]

see #11559 (comment)

[DetachHead]

i have no idea what i'm doing lol

[sobolevn]

Can you please explain your idea behind this PR? Maybe I can help you 🙂

[sobolevn]

This file is just synced from here: https://github.com/python/typeshed/blob/master/stdlib/_typeshed/__init__.pyi

Manually updating it is not a good practice.

[sobolevn]

We don't use _typeshed. types in mypy right now. It would be hard to test.

[DetachHead]

@sobolevn i'm trying to make ellipsis private to fix #11559 but i have no idea how. apparently it's a more difficult problem than i thought? see python/typeshed#3556

[sobolevn]

Yes, this is going to be hard 🙂

What I can see here:

1. A way to make _typeshed discoverable during module graph builder
2. Maybe we would need to special case it in semanal.py as we do with typing and typing_extensions
3. We need to think how to test it. Right now mypy uses the bare minimum for each test. This is made to run tests faster. 3rd party modules are not supported. So, probably we would either need to allow _typeshed or to use an extra fixture.
4. Finally, we need to consult core-devs if everything is right. This is going to be a really big change! But, a very useful one. There are other cases when we can use _typeshed types: NoneType, SupportsWrite, etc.

[hauntsaninja]

ellipsis is type_check_only in typeshed these days and the problem will go away on its own on Python 3.10 and newer thanks to types.EllipsisType

[DetachHead]

it's only marked as type_check_only in <=3.9. in 3.10, you don't get a type error when trying to use it even though it crashes at runtime on both versions, so i don't see how the problem will go away on its own?

• 3.9
• 3.10

# builtins.pyi

if sys.version_info >= (3, 10):
    from types import EllipsisType

    # Backwards compatibility hack for folks who relied on the ellipsis type
    # existing in typeshed in Python 3.9 and earlier.
    ellipsis = EllipsisType

    Ellipsis: EllipsisType

else:
    # Actually the type of Ellipsis is <type 'ellipsis'>, but since it's
    # not exposed anywhere under that name, we make it private here.
    @final
    @type_check_only
    class ellipsis: ...

    Ellipsis: ellipsis

[hauntsaninja]

We'll remove it in typeshed next year when 3.9 is goodbye python/typeshed#11223 (comment)

[DetachHead]

i'm confused as to why this "backwards compatibility hack" for python 3.9 is in the if sys.version_info >= (3, 10) condition? and is that the one that's getting removed or is it the else condition? or is there something i'm missing?

[hauntsaninja]

in a year it will look like this:

from types import EllipsisType
Ellipsis: EllipsisType

i've seen codebases where people relied on ellipsis to type ellipsis, a little niche, but gives them a way to spell their type check