Improve typing of handlers

[marcuslimdw]

Currently, handlers are typed permissively e.g. on_change is typed Optional[Callable[..., Any]]. This provides a poor DX because autocomplete and type checking don't work as well.

I propose the following:

1. Define a new type Handler (see below).
2. Use this type to annotate handler arguments - for example, on_change would now be annotated Handler[ValueChangeEventArguments]

from typing import Any, Callable, Optional, TypeAlias, TypeVar, Union

EventT = TypeVar("EventT")
Handler: TypeAlias = Optional[Union[Callable[[EventT], Any], Callable[[], Any]]]

[falkoschindler]

Thank for bringing this up, @marcuslimdw!
I like the idea of improving type annotations for event handlers.

The only downside I see in using type aliases might be that they "hide" the type behind the alias "Handler[ClickEventArguments]":

But I guess this is better than "Callable[..., Any]". And it is widely known that a "handler" is a kind of callable.

Would you like to create a pull request? 🙂

[falkoschindler]

PR #3811 has just been released.