Make request.state generic

[patrick91]

Hi there!

I was playing around with request.state, and I was wondering if we could make it generic, so that users can get better autocomplete on it (and maybe a bit of type safety too).

The way this would work is where you accept a Request you could also do Request[MyStateType], and request.state would be of type MyStateType

I think we can implement this in a backwards compatible way if we use TypeVar from typing extensions with a default value of any, like this:

from typing import Any
from typing_extensions import TypeVar

RequestState = TypeVar("RequestState", default=Any)  # this could also be `State`

This means that any current code wouldn't throw an error, and power users could type the state var 😊

The only issue I see at the moment is that State is a wrapper on a dict, but doesn't provide getitem, and my assumption is that types for State would be TypedDicts 😊 but is should be easy to add support for that. But I'm also saying this without knowing the reason why the state is a class on top of a dict, so I might be wrong :D

[Kludex]

Check #2218. We're trying...

[Kludex]

python/typing#1457 🤷‍♂️

[patrick91]

@Kludex what's the reason why the state is not kept as a proper dictionary? 😊

[Kludex]

It was like this before, and now changing that is a breaking change

[patrick91]

I hope I'm not being annoying, but I wonder if we could make it work also as a dict, so we keep the old behaviour but we get better type safety by making Request generic, like here: https://github.com/encode/starlette/pull/2218/files

but we also add __getitem__ on state 😊