Shared via mypy Playground

main.py

from typing import Literal, reveal_type

def sign(x: int) -> Literal[-1, 0, 1]:
    """Extracts the sign of x."""
    s = -1 if x < 0 else (0 if x == 0 else 1)
    reveal_type(s)  # int
    match s:
        case -1 | 0 | 1:
            reveal_type(s)  # narrowed to Literal[-1, 0, 1]
            return s
        case _:
            raise AssertionError("Unreachable.")