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Optional static typing for Python
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`unreachable` false positive when using `isinstance` on class with `__call__` when function parameter uses `ParamSpec` #16024

Open DetachHead opened 1 year ago

DetachHead commented 1 year ago 
from typing import Callable, ParamSpec

P = ParamSpec("P")

class Foo:
    def __call__(self) -> None:
        ...

def foo(fn: Callable[P, None]) -> None:
    if isinstance(fn, Foo):
        print("reached") # error: Statement is unreachable  [unreachable]

foo(Foo())

playground

in this example, that line is always reached at runtime

DetachHead commented 1 year ago

minified further:

from typing import Callable

def foo(fn: Callable[[], object]) -> None:
    if isinstance(fn, type):
        print(fn)