ruff/crates/red_knot_python_semantic/resources/mdtest/generics.md

PEP 695 Generics

Class Declarations

Basic PEP 695 generics

class MyBox[T]:
    data: T
    box_model_number = 695

    def __init__(self, data: T):
        self.data = data


# TODO not error (should be subscriptable)
box: MyBox[int] = MyBox(5)  # error: [non-subscriptable]
# TODO error differently (str and int don't unify)
wrong_innards: MyBox[int] = MyBox("five")  # error: [non-subscriptable]
# TODO reveal int
reveal_type(box.data)  # revealed: @Todo

reveal_type(MyBox.box_model_number)  # revealed: Literal[695]

Subclassing

class MyBox[T]:
    data: T

    def __init__(self, data: T):
        self.data = data


# TODO not error on the subscripting
class MySecureBox[T](MyBox[T]): ...  # error: [non-subscriptable]


secure_box: MySecureBox[int] = MySecureBox(5)
reveal_type(secure_box)  # revealed: MySecureBox
# TODO reveal int
reveal_type(secure_box.data)  # revealed: @Todo

Cyclical class definition

In type stubs, classes can reference themselves in their base class definitions. For example, in typeshed, we have class str(Sequence[str]): ....

This should hold true even with generics at play.

class Seq[T]: ...


# TODO not error on the subscripting
class S[T](Seq[S]): ...  # error: [non-subscriptable]


reveal_type(S)  # revealed: Literal[S]