A base type for annotations?

[Dreamsorcerer]

I don't think this is possible currently, but it would be useful for Generics etc. if there was some way to specify type[T] for any valid annotation, to be used at runtime.

For example, we have aiohttp.web.AppKey defined like:

class AppKey(Generic[T]):
    def __init__(self, name: str, t: type[T]):

expected to be used like AppKey("foo", int) to define the type for the key (mostly imitating the design of TypeVar).

The problem is that a lot of valid typing annotations are not actual 'types' and produce a typing error (e.g. AppKey(..., Callable)). There is probably some issue with making all of these compatible with type, but maybe we could introduce a new thing for types of typing constructs? Then we can annotate it like type[T] | annotation_type[T] or something.

[Gobot1234]

This was something I wanted to fix in a future pep for reified types

[JelleZijlstra]

This sounds like you want TypeForm: python/mypy#9773. That proposal hasn't progressed much, though.