Try to make Request generic over State

[adriangb]

#2065 (comment)

TODO: how do we let users at runtime customize the state creation function? Currently, Starlette creates the Request object so it can't be as simple as a constructor parameter. For FastAPI I suppose it could introspect the type hints to get the generic argument.

[adriangb]

@Kludex any idea how to get this to work nicely with mypy?

[Kludex]

@Kludex any idea how to get this to work nicely with mypy?

I think I have some comments around about it. I'll look later, and share it here. (It maybe in our WhatsApp conversation... I'll check.)

[Kludex]

I've created python/typing#1457.

[michaeloliverx]

On an semi related side note I hacked around this in FastAPI by doing this:

from collections.abc import AsyncGenerator
from contextlib import asynccontextmanager
from typing import Annotated, TypedDict, cast

from fastapi import Depends, FastAPI, Request


class State(TypedDict):
    foo: str
    bar: str


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[State, None]:
    ...


async def get_state(request: Request) -> State:
    return cast(State, request.state._state)


StateDependency = Annotated[State, Depends(get_state)]

[Kludex]

I'll close this, since the Python type system still doesn't support this.

• We can watch How to convert `TypedDict` to a `dataclass_transform` behavior? python/typing#1457 and related discussions.