How to deal with this Pylance type error regarding the exception handler?

[vagreargnatry]

My code is as follows:

import uvicorn
from starlette.applications import Starlette
from starlette.exceptions import HTTPException
from starlette.requests import Request
from starlette.responses import JSONResponse
from starlette.routing import Route


def hello(request: Request):
    raise HTTPException(status_code=400, detail="test for exception handler")
    return JSONResponse({"message": "Hello!"})


# https://www.starlette.io/exceptions/#errors-and-handled-exceptions
async def handle_error(request: Request, exc: HTTPException) -> JSONResponse:
    return JSONResponse({"detail": exc.detail}, status_code=exc.status_code)


exception_handlers = {
    HTTPException: handle_error,
}


routes = [
    Route("/", hello),
]

app = Starlette(
    debug=True,
    routes=routes,
    exception_handlers=exception_handlers,  # <- Pylance type error (line 31)
)

if __name__ == "__main__":
    uvicorn.run("main:app", reload=True)

Pylance is throwing an error on line 31. The error message is as follows:

Argument of type "dict[type[HTTPException], (request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]]" cannot be assigned to parameter "exception_handlers" of type "Mapping[Any, ExceptionHandler] | None" in function "__init__"
  Type "dict[type[HTTPException], (request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]]" cannot be assigned to type "Mapping[Any, ExceptionHandler] | None"
    "dict[type[HTTPException], (request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]]" is incompatible with "Mapping[Any, ExceptionHandler]"
      Type parameter "_VT_co@Mapping" is covariant, but "(request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]" is not a subtype of "ExceptionHandler"
        Type "(request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]" cannot be assigned to type "ExceptionHandler"
          Type "(request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]" cannot be assigned to type "HTTPExceptionHandler"
          Type "(request: Request, exc: HTTPException) -> Coroutine[Any, Any, JSONResponse]" cannot be assigned to type "WebSocketExceptionHandler"
    Type cannot be assigned to type "None"

At present, the functionality of the exception handler is normal; the test content is as follows:

curl http://127.0.0.1:8000/ -i

HTTP/1.1 400 Bad Request
Content-Length: 39
Connection: keep-alive
Content-Type: application/json
Date: Tue, 12 Dec 2023 08:44:29 GMT
Keep-Alive: timeout=4
Proxy-Connection: keep-alive
Server: uvicorn

{"detail":"test for exception handler"}

[vagreargnatry]

I've got it. The type annotation for the second parameter of handle_error should be Exception, not HTTPException.

async def handle_error(request: Request, exc: Exception) -> JSONResponse:
    return JSONResponse({"info": str(exc)}, status_code=500)

But I want to annotate the second parameter of handle_error as HTTPException without triggering Pylance errors. What should I do?

[vagreargnatry]

This piece of code utilizes assert to change the type of the variable exc, preventing Pylance from raising errors. Is this approach appropriate? Are there better alternatives?

from typing import Annotated

import uvicorn
from pydantic import BaseModel, StringConstraints, ValidationError
from starlette.applications import Starlette
from starlette.requests import Request
from starlette.responses import JSONResponse, PlainTextResponse
from starlette.routing import Route


class DirectJsonResponse(JSONResponse):
    def render(self, content: bytes) -> bytes:
        return content


Name = Annotated[str, StringConstraints(min_length=3, max_length=12)]


class Info(BaseModel):
    name: Name


async def hello(request: Request):
    req_body = Info.model_validate(await request.json())
    return PlainTextResponse(f"Hello, {req_body.name}!")


async def validation_error_handler(request: Request, exc: Exception) -> JSONResponse:
    assert type(exc) == ValidationError  # use assert to change type of `exc`
    return DirectJsonResponse(exc.json().encode(), status_code=400)


exception_handlers = {
    ValidationError: validation_error_handler,
}


routes = [
    Route("/", hello, methods=["POST"]),
]

app = Starlette(
    debug=True,
    routes=routes,
    exception_handlers=exception_handlers,
)

if __name__ == "__main__":
    uvicorn.run("main:app", reload=True)

[vagreargnatry]

After the automatic update of the Python plugin in VSCode, it no longer throws errors.