Check that statement or expression is unreachable [unreachable]

If you use —warn-unreachable, mypy generates an error if itthinks that a statement or expression will never be executed. In most cases, this is due toincorrect control flow or conditional checks that are accidentally always true or false.

# mypy: warn-unreachable
 
def example(x: int) -> None:
    # Error: Right operand of 'or' is never evaluated  [unreachable]
    assert isinstance(x, int) or x == 'unused'
 
    return
    # Error: Statement is unreachable  [unreachable]
    print('unreachable')