typing.is_typeddict returns False for generic TypedDict specializations

[semohr]

Bug report

Bug description:

It appears that typing.is_typeddict returns False when called on a specialized TypedDict that is used as a type parameter in a generic TypedDict. This behavior is not documented and seems unexpected.

from typing import is_typeddict, Generic, TypeVar, TypedDict

A = TypeVar("A", bound=TypedDict)

class Attributes(TypedDict):
    title: str

class Resource(TypedDict, Generic[A]):
    a: A 

print(is_typeddict(Resource[Attributes]))
# False (unexpected)

is_typeddict(Resource[Attributes]) should return True, since Resource[...] is still a TypedDict after specialization.

---

I reported this initially in python/typing#2280 where it was suggested I open an issues here.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

[JelleZijlstra]

The current behavior is consistent with other similar functions:

>>> class P[T](typing.Protocol): ...
... 
>>> typing.is_protocol(P)
True
>>> typing.is_protocol(P[int])
False
>>> import inspect
>>> inspect.isclass(list[int])
False
>>> inspect.isclass(list)
True
>>> inspect.isclass(list[int])
False

The rationale is that an object like list[int] is a generic alias (either types.GenericAlias or typing._GenericAlias), not a class itself. A generic alias like Resource[Attribute] in your example does not have the runtime attributes that a TypedDict class has, such as __required_keys__.