Open
Description
We shouldn't require @final
decoration for TypedDicts to narrow them based on the 'in' operator.
Why?
Basically @erictraut's comment.
In #13838, we've added "key in Union[TypedDict, ...]" narrowing for TypedDicts that are marked @final
. The reason was to prevent this:
class Mammal(TypedDict):
mammary_glands: int
class Bird(TypedDict):
eggs: int
class Echidna(Mammal):
eggs: int
animal: Mammal | Bird
if 'eggs' in animal:
assert_type(animal, Bird) # WRONG! Could still be a Mammal (a Echidna)
if 'eggs' in animal and 'mammary_glands' in animal:
assert_never(animal) # WRONG! Could still be a Mammal (a Echidna)
However, per @erictraut's comment, due to TypedDict being a structural type, we shouldn't consider the class hierarchy when type-matching.
This will be consistent with pyright and TypeScript (Playground Link).