pow float return value is Any in 0.950

[TylerYep]

Bug Report

I upgraded to mypy 0.950 today and ran into the following error involving function return types:

To Reproduce

# x.py
def fn(x: float = 8.9) -> float:
    return 2 ** x    # error: Returning Any from function declared to return "float"  [no-any-return]

Expected Behavior

Expected this to pass cleanly.

Actual Behavior

I'm not sure why this now returns Any.

Your Environment

• Mypy version used: 0.950
• Mypy configuration options from mypy.ini (and other config files): strict = True
• Python version used: Python 3.10.0
• Operating system and version: Mac OSX

[TylerYep]

Similarly,

from typing import Generic, TypeVar

T = TypeVar("T")


class Animal(Generic[T]):
    pass


class Pooh(Animal[T]):
    pass


class Tigger(Animal[T]):
    pass


def build_friend(animal_type: str) -> Animal[T]:
    friend_map = {constructor.__name__: constructor for constructor in (Pooh, Tigger)}
    return friend_map[animal_type]()     
    # error: Incompatible return value type (got "object", expected "Animal[T]")  [return-value]

[AlexWaygood]

Could you open a separate issue about the second thing? It looks like a completely different problem.

Issue number 1 looks like a pretty clear consequence of #7047 (cc. @JelleZijlstra). We might be able to make the types more specific by adding yet another overload to int.__pow__ or float.__rpow__. I can create a PR in the morning.

[Akuli]

int ** float can be a complex number, if the int is negative.

>>> (-1) ** 2.3
(0.587785252292474+0.8090169943749468j)

But this doesn't happen for 2 ** float, or for any other positive number instead of 2:

>>> 2 ** (-3.4)
0.09473228540689989

0 ** float behaves a bit surprisingly, and I don't think we should handle it specially in the stubs. In practice, the 0 is very unlikely to be specified in a way where the type checker can infer its type to be Literal[0].