using Optional in TypedDict provides not consistent behaviour with PEP 589

[Paweł Małecki]

Example Code

from typing_extensions import TypedDict
from typing import Optional


class A(TypedDict):
    x: Optional[int]

class B(TypedDict):
    x: int

def f(a: A) -> None:
    a['x'] = None

b: B = {'x': 0}
f(b)  # Type check error: 'B' not compatible with 'A'
b['x'] + 1  # Runtime error: None + 1

Expected Behavior

error: incompatible type argument in function f

Actual Behavior

Success: no errors found

Example works as expected in mypy.

[Rebecca Chen]

Agreed, pytype should flag this. We (the pytype devs) discussed this briefly, and we probably want to match mutable and immutable container types differently.