Slots can return any object

[altendky]

There is no requirement that slots return specifically None, any object will do.

[BryceBeagle]

Can this not be Callable[..., Any] or even just plain Callable?

[altendky]

Any means that you can do anything you want with the value which isn't a good default since you don't know what it will be. object means it can be any object and you can only expect to do things to it that you can do with object, which is mostly the case (pending objects that block access to object features).

In this case it probably doesn't make much difference, but object is a more sensible default as it doesn't effectively disable type hints. Bare typing.Callable just defaults to the Any.

[The-Compiler]

I'm not really convinced object (over Any) is the right thing to do here - that being said, I've never used slot return values. But surely you'd usually know what type you get from a specific slot and then do things based on that type? If you get object back, like you say, you pretty much can't do anything with the return value, no?

[altendky]

object forces you, the only person that has any basis for knowing, to explicitly state that you know via a typing.cast(). Any leaves you ignorantly passing type hint checks even if you erroneously use the result as if it is two different types.

But does this hint leak back out to anything outside? My impression was that it just describes what sorts of things are accepted in various places that need a slot. I think the next layer is to get into Generics so that we can actually relate the type of the incoming callable and properly hint the outputs. But I haven't even started to think about where or how that would look. I expect that to be a tough task.