strict mode in zip causes extra type errors

[Molkree]

Environment data

• Language Server version: v2021.9.4
• OS and version: Win10
• Python version (& distribution if applicable, e.g. Anaconda): 3.10

Expected behaviour

No error warnings.

Actual behaviour

Below code doesn't cause any warnings:

names = ["John", "Jess"]
ages = [20]
for name, age in zip(names, ages):
    pass

However when using the new strict mode for zip function added in Python 3.10 (PEP 618):

names = ["John", "Jess"]
ages = [20]
for name, age in zip(names, ages, strict=True):
    pass

I am getting 3 errors now:

• 1 on zip function itself, this appears with type checking at basic
  No overloads for "__new__" match the provided arguments
Argument types: (list[str], list[int], Literal[True])
• strict type checking also introduces errors for each unpacked variable:
  Type of "name"/"age" is unknown

Code Snippet / Additional information

Additionally, strict is not in the candidates list when typing in zip.

[jakebailey]

The stub for zip is here: https://github.com/python/typeshed/blob/master/stdlib/builtins.pyi#L1327

It appears as though it hasn't yet been updated for PEP 618 yet.

[Molkree]

This was just fixed in typeshed.

[jakebailey]

Thanks. This will be included in our next release.

[jakebailey]

This issue has been fixed in version 2021.10.0, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/main/CHANGELOG.md#2021100-6-october-2021

[Molkree]

I no longer see any errors when using strict however it is still not in the candidates list.

Not sure if it's on the typeshed or pylance side and I understand it's not really the initial issue so I can open a new one.

[jakebailey]

That seems like a bug in the completion provider; zip is unique because it's signatures are provided by __new__ and they are a little duplicated thanks to the lack of variadics. It could be that we don't handle this right; I did notice that signature help didn't work correctly with zip too.

Would you mind filing a new issue?

[Molkree]

Would you mind filing a new issue?

Sure, I've opened #1912.