Inner function does not preserve narrowed type

[mflova]

Summary

Mypy and pyright apparently do not have this problem. In my example below, obj from inner_func is guaranteed to be a type string. This can also be seen in the first reveal_type. However, it seems that ty is taking the type of obj to be the input argument one (int | str) instead of the narrowed down (str)

from collections.abc import Mapping
from typing import Any
from typing_extensions import reveal_type


def func(obj: int | str) -> None:
    obj = str(obj) if isinstance(obj, int) else obj
    reveal_type(obj)  #  str

    def inner_func():
        reveal_type(obj)  # int | str

Version

0.0.1-alpha.19

[sharkdp]

Thank you for reporting this.

This is a known limitation that is documented in these tests. We currently do not yet analyze the control flow in the outer function to the extend that it would allow us to infer that the narrowing inside inner_func is safe for all calls to it. For example, narrowing would be unsafe if the body of the func function would continue like this:

    obj = 1
    inner_func()

[mtshiba]

astral-sh/ruff#19932 addresses this issue.