False positive unbound variables though all cases are checked with isinstance

[Andrej730]

False positive unbound variables, see example below:

class A: ...
class B: ...

# works fine
def test_1(obj: A | B) -> None:
    if isinstance(obj, A):
        new_name = "test"
    elif isinstance(obj, B):
        new_name = "test"
    a = new_name


# breaks
def get_obj() -> A | B: ...
def test_2() -> None:
    obj = get_obj()
    if isinstance(obj, A):
        new_name = "test"
    elif isinstance(obj, B):
        new_name = "test"
    # "new_name" is possibly unbound
    a = new_name

[erictraut]

Pyright is working as designed here, so this isn't a bug.

See this documentation for limitations on "implied else" narrowing.

[Andrej730]

Okay, I guess a function return type is too implicit for this :(
As a workaround obj: A | B = get_obj() seems to work fine.