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I'm sure there's a limit to how far type inference can go, and it's reasonable that it doesn't evaluate the result of applying an index:
from typing import *
def f(x: Dict[str, Union[int, str]], k: str) -> None:
if isinstance(x[k], int):
x[k] + 1 # type error: Unsupported operand types for + ("Union[int, str]" and "int")
But maybe an example in the docs would be helpful? A suggestion could be given to either rewrite it like this:
def f(x: Dict[str, Union[int, str]], k: str) -> None:
v = x[k]
# note: both x[k] (in the if expression and in the body) must be replaced with a simple variable
if isinstance(v, int):
v + 1 # no type error
or to just mark it as # type: ignore.
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