raise TypeError(f"{self} is not subscriptable")
@_SpecialForm
def ClassVar(self, parameters):
    """Special type construct to mark class variables.
    An annotation wrapped in ClassVar indicates that a given
    attribute is intended to be used as a class variable and
    should not be set on instances of that class.
    Usage::
        class Starship:
            stats: ClassVar[dict[str, int]] = {} # class variable
            damage: int = 10                     # instance variable
    ClassVar accepts only types and cannot be further subscribed.
    Note that ClassVar is not a class itself, and should not
    be used with isinstance() or issubclass().
    """
    item = _type_check(parameters, f'{self} accepts only single type.')
    return _GenericAlias(self, (item,))
@_SpecialForm
def Final(self, parameters):
    """Special typing construct to indicate final names to type checkers.
    A final name cannot be re-assigned or overridden in a subclass.
    For example::
        MAX_SIZE: Final = 9000
        MAX_SIZE += 1  # Error reported by type checker
        class Connection:
            TIMEOUT: Final[int] = 10
        class FastConnector(Connection):
            TIMEOUT = 1  # Error reported by type checker
    There is no runtime checking of these properties.
    """
    item = _type_check(parameters, f'{self} accepts only single type.')
    return _GenericAlias(self, (item,))
@_SpecialForm
def Union(self, parameters):
    """Union type; Union[X, Y] means either X or Y.
    On Python 3.10 and higher, the | operator
    can also be used to denote unions;