Is it possible to infer types for add_task via typing.ParamSpec?

[jd-solanki]

Hi 👋🏻

Great fan of encode ❤️

As python type system is improving can we use typing.ParamSpec somehow to infer the type for arguments we need to pass to add_task callable?

Right now, If we write this: .add_task(my_task, |) then we don't get any type hints at | about what arguments my_task accepts.

I'm not type wizard but if typing.ParamSpec can infer types of callback (first arg) then it'll nice addition.

Thanks 😇

[Kludex]

We do use it... https://github.com/encode/starlette/blob/master/starlette/background.py

[jd-solanki]

I was trying it in FastAPI and main goal was to get the autocompletion for the params but it looks like we aren't getting that is that expected?

import time

from fastapi import BackgroundTasks, FastAPI

app = FastAPI()


def background_task(*, message: str):
    time.sleep(3)
    print(message)


@app.get("/")
async def read_root(background_tasks: BackgroundTasks):
    background_tasks.add_task(background_task, message="Hello, World!")
    return {"message": "Hello, World!"}

I think this will be same with starlette 🤔

[jd-solanki]

Here's starlette example:

import time

from starlette.applications import Starlette
from starlette.background import BackgroundTask
from starlette.requests import Request
from starlette.responses import JSONResponse
from starlette.routing import Route


def background_task(*, message: str):
    time.sleep(3)
    print(message)


async def homepage(request: Request) -> JSONResponse:
    task = BackgroundTask(background_task, message="hello")
    return JSONResponse({"hello": "world"}, background=task)


app = Starlette(
    debug=True,
    routes=[
        Route("/", homepage),
    ],
)

P.S. You been to india? when?

[Kludex]

It works here.

P.S. You been to india? when?

Yep, last year. I was invited to give a talk in Hyderabad. 🙏

[jd-solanki]

Yes, We're getting type error in my example as well so that's working.

Can we make it work with autocompletion as well?

[Kludex]

I think that's on the IDEs/language server's side...