correct syntax for variable annotation that should fail at runtime in a certain manner more examples are in testgrammar and testparser this one is ok as proposed by guido
def f_bad_ann():
    __annotations__[1] = 2

class C_OK:
    def __init__(self, x: int) -> None:
        self.x: no_such_name = x  

class D_bad_ann:
    def __init__(self, x: int) -> None:
        sfel.y: int = 0

def g_bad_ann():
    no_such_name.attr: int = 0