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## Summary `__class_getitem__` is [implicitly a classmethod](https://docs.python.org/3/reference/datamodel.html#object.__class_getitem__). ## Test Plan Added regression test.
2.5 KiB
2.5 KiB
Class subscript
Class getitem unbound
class NotSubscriptable: ...
# error: "Cannot subscript object of type `<class 'NotSubscriptable'>` with no `__class_getitem__` method"
a = NotSubscriptable[0]
Class getitem
class Identity:
def __class_getitem__(cls, item: int) -> str:
return str(item)
reveal_type(Identity[0]) # revealed: str
__class_getitem__ is implicitly a classmethod, so it can be called like this:
reveal_type(Identity.__class_getitem__(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: <class 'A'> | <class '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: [non-subscriptable] "Cannot subscript object of type `<class 'Spam'>` with no `__class_getitem__` method"
# revealed: str | Unknown
reveal_type(Spam[42])
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[1]` with no `__getitem__` method"
reveal_type(a) # revealed: str | Unknown
Intersection of nominal-instance types
If a subscript operation could succeed for any positive element of an intersection, no diagnostic should be reported even if it would not succeed for some other element of the intersection.
class Foo: ...
class Bar:
def __getitem__(self, key: str) -> int:
return 42
def f(x: Foo):
if isinstance(x, Bar):
# TODO: should be `int`
reveal_type(x["whatever"]) # revealed: @Todo(Subscript expressions on intersections)