Typing for the @before hook function arguments.

[0x1618]

Hello, is it possible to make a type-safe @before hook so that the arguments passed to the hook function are typed? Can I just use my own decorator instead of @before?

[vytas7]

Hi @0x1618!
We have already improved the typing of hooks somewhat using ParamSpec and Concatenate, but the improvement is not a part of any stable release yet.

Could you try installing the development version, and see if that helps?

$ pip install git+https://github.com/falconry/falcon/

To answer the second part of your question, you can absolutely use your own decorators, or any other Python paradigm, on responder methods, as long as they retain the naming pattern and stay callable.

[0x1618]

Yes, the development version works perfectly for this case. However, I cannot get my own decorator to work. I keep getting a 405 Method Not Allowed (even if the method is correct) error no matter what I try. I’m probably doing something wrong. Can you provide a documentation reference or a simple example of how to decorate a route?

[vytas7]

I don't think we have a good example for that in the docs... I created an issue: #2533.

For the time being, the following snippet seemed to work for me:

import functools
import logging
from typing import Any, Callable, Concatenate, ParamSpec

from falcon import App, Request, Response

logging.basicConfig(
    format='%(asctime)s [%(levelname)s] %(message)s', level=logging.INFO)


_P = ParamSpec('_P')


def log_access(
        responder: Callable[Concatenate[Any, Request, Response, _P], None]
) -> Callable[Concatenate[Any, Request, Response, _P], None]:

    @functools.wraps(responder)
    def wrapper(rsrc: object, req: Request, resp: Response, /,
                *args: _P.args, **kwargs: _P.kwargs) -> None:
        responder(rsrc, req, resp, *args, **kwargs)
        logging.info(f'[{type(rsrc).__name__}] {req.method} {req.relative_uri}'
                     f' => HTTP {resp.status_code}')

    return wrapper


class HelloResource:
    @log_access
    def on_get(self, req: Request, resp: Response) -> None:
        resp.media = {
            'message': 'Hello, decorators!',
            'params': req.params,
        }

    @log_access
    def on_get_name(self, req: Request, resp: Response, name: str) -> None:
        resp.media = {
            'message': f'Hello, {name}!',
            'params': req.params,
        }


app = App()
app.add_route('/hello', HelloResource())
app.add_route('/hello/{name}', HelloResource(), suffix='name')

[0x1618]

oh, my bad... I did async def log_access, but it should be def log_access and the wrapper is only async.