ruff/crates/ty_python_semantic/resources/mdtest/subscript/class.md

Class subscript

Class getitem unbound

class NotSubscriptable: ...

a = NotSubscriptable[0]  # error: "Cannot subscript object of type `Literal[NotSubscriptable]` with no `__class_getitem__` method"

Class getitem

class Identity:
    def __class_getitem__(cls, item: int) -> str:
        return str(item)

reveal_type(Identity[0])  # revealed: str

Class getitem union

def _(flag: bool):
    class UnionClassGetItem:
        if flag:
            def __class_getitem__(cls, item: int) -> str:
                return str(item)
        else:
            def __class_getitem__(cls, item: int) -> int:
                return item

    reveal_type(UnionClassGetItem[0])  # revealed: str | int

Class getitem with class union

def _(flag: bool):
    class A:
        def __class_getitem__(cls, item: int) -> str:
            return str(item)

    class B:
        def __class_getitem__(cls, item: int) -> int:
            return item

    x = A if flag else B

    reveal_type(x)  # revealed: Literal[A, B]
    reveal_type(x[0])  # revealed: str | int

Class getitem with unbound method union

def _(flag: bool):
    if flag:
        class Spam:
            def __class_getitem__(self, x: int) -> str:
                return "foo"

    else:
        class Spam: ...
    # error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[Spam, Spam]` is possibly unbound"
    # revealed: str
    reveal_type(Spam[42])

TODO: Class getitem non-class union

def _(flag: bool):
    if flag:
        class Eggs:
            def __class_getitem__(self, x: int) -> str:
                return "foo"

    else:
        Eggs = 1

    a = Eggs[42]  # error: "Cannot subscript object of type `Literal[Eggs] | Literal[1]` with no `__getitem__` method"

    # TODO: should _probably_ emit `str | Unknown`
    reveal_type(a)  # revealed: Unknown