[Feature Request] A "@dash.typed_callback" that plays more nicely with MyPy than "@dash.callback"

[odorikakeru]

What I Want
The projects I work on include MyPy in the testing pipeline. For "quality of life" and code readability reasons I am on a mission to reduce the need for `# type: ignore" style comments as much as possible

Proposed Solution
In my current project I am using the following wrapper:

Params = ParamSpec('Params')
ReturnVar = TypeVar('ReturnVar')
Func = Callable[Params, ReturnVar]

def typed_callback(app: Dash, *args: Any, **kwargs: Any) -> Callable[[Func], Func]:
    return cast(Callable[[Func], Func], app.callback(*args, **kwargs))

I have forked the dev branch and added a typed_callback function (here: _callback.py) as a proof of concept.

I would like feedback on this idea.

(Disclosure: the tests in my fork were generated using AI)

[T4rk1n]

I'd rather we add typing to the existing callback function, we already type it as

dash/dash/_callback.py

Line 84 in d2e5bbe

) -> Callable[..., Any]:

Maybe simply adding those TypeVar's in instead of the ..., Any would be good if not supplying those don't generate an error on it's own and infer that as Callable[..., Any].

[odorikakeru]

I'd rather we add typing to the existing callback function, we already type it as

dash/dash/_callback.py

Line 84 in d2e5bbe

) -> Callable[..., Any]:
Maybe simply adding those TypeVar's in instead of the ..., Any would be good if not supplying those don't generate an error on it's own and infer that as Callable[..., Any].

Thanks for your comment, this is exactly the sort of thing that I was unsure about.

Updating callback(...) would be my preference, too, but I was erring on the side of caution. If people have a linter like MyPy in their CI/CT pipeline then changing type definitions can mess things up for them (ex: in my pipeline "unnecessary # type: ignore" will block commits).

If there is a warning of change of behaviour then definitely having one reliable function is much better than two.

[T4rk1n]

Updating callback(...) would be my preference, too, but I was erring on the side of caution. If people have a linter like MyPy in their CI/CT pipeline then changing type definitions can mess things up for them (ex: in my pipeline "unnecessary # type: ignore" will block commits).

We have the typing compliance tests for that, if adding those type definition passes the tests I think they can be added. Otherwise we can add more type definition in a major version update.