I want to know the Origin of an annotation. This works fine for basically everything, but there is no way to check if an annotation is a TypedDict subclass without resorting to (semantically) private API (by checking if it is an instance of_TypedDictMeta), becauseissubclass(x, TypedDict) fails. I believe this is because you don't want people thinkingisinstance(x, TypedDict) will work to actually validate the keys on a dict. However, I don't think there's any reason to preventissubclass on it

https://github.com/python/cpython/blob/1b4552c/Lib/typing.py#L1901

Here is an example use-case:

fromtypingimportDict,get_origindefvalidate(data,annotation)->bool:"""check if `data` conforms to the type given in `annotation`"""# this worksifget_origin(annotation)isDict:returnisinstance(data,dict)# but this doesn't...elifis_a_typed_dict(annotation):returnisinstance(data,dict)andvalidate_typeddict_keys(data,annotation)    ...

This could be solved in one of the following ways:

• allowissubclass onTypedDicts
  • or allow it only onTypedDict itself and not subclasses of it, e.g. using a_root classvar likeNamedTuple does for its magic
    • although I see no reason not to allow it in that case either
• make_TypedDictMeta public API (rename toTypedDictMeta)
• makeget_origin work onTypedDicts (not ideal because it isn't really a type)