Create app.timer for timing UI-independent functions

[falkoschindler]

As discussed in #3187, ui.timer works like a UI element: It starts running when a page is created and stops when removing the timer or its parent container. This is handy in some cases, but isn't very helpful in others.

Therefore we propose an app.timer function that behaves similar to ui.timer, but runs on an app level, independent of connected clients. It will, however, have no UI context to work with. So it is primarily meant to run non-UI code.

[v479038280]

any progress？

[falkoschindler]

Good question!
I took the opportunity to create PR #4091 implementing this feature, borrowing some code from RoSys.
There shouldn't be too much work left, so we might be able to release it in upcoming version 2.9.

[thetableman]

I know I'm a bit late to the party, given that a PR is already in the works, but I've been using a variant of this package along with an @app.on_startup(...) to automate a regular background process.

https://fastapi-utils.davidmontague.xyz/user-guide/repeated-tasks/#the-repeat_every-decorator

I do like the idea of the timer being implemented as a decorator function versus how I expect the version in the PR will work.

[falkoschindler]

That's a great idea, @thetableman!
I don't think a decorator contradicts PR #4091. It could be an extension so that you can either use app.timer like ui.timer (in fact one is deriving from another) or @app.repeat_every(...). If repeat_every would use app.timer internally, it would automatically run on startup (or immediately if the app is already running).

[falkoschindler]

Simply adding

def repeat_every(self, seconds: float) -> Callable:
    """Decorator to repeat a function every `seconds` seconds."""
    def decorator(func: Callable) -> Callable:
        self.timer(seconds, func)
        return func
    return decorator

to app.py seems to work.

[rodja]

Should we add this feature in another pull request?

[thetableman]

Another thought, perhaps for a later version, would be to extend this proposed app level timer capabilities to run functions at specific times.

A simpler implementation might allow a user to just schedule a function at 6.00am each day whilst a more advanced version might allow for every Tuesday at 6.00am or the 15th of every Month.

[falkoschindler]

That would be nice, but maybe out of scope of a UI framework. You could use packages like schedule for this purpose.

[thetableman]

True... but schedule also supports running a function at a timed interval (schedule.every(10).minutes.do(job)) so wouldn't that then negate the need for developing a custom app.timer function?

[falkoschindler]

Valid point. In our applications, especially our robot systems, we often need to run callbacks every x seconds to read sensors, update internal state etc. So it is very convenient to have such timers built into NiceGUI - like setTimeout and setInterval in JavaScript. For scheduling callbacks for a certain time of day, we created an application-specific schedule module which also takes sunrise and sunset times into account. Requirements can vary between applications, which is why we didn't move it to NiceGUI.
What I'm trying to say: Looping or delaying with a simple interval given in seconds is a relatively straight-forward requirement covering the majority of use cases. But we'll consider adding some kind of simple schedule feature in the future. 👍

[falkoschindler]

app.timer has just been released in NiceGUI 2.9. 🚀

Let's discuss ideas like @app.repeat_every and scheduling function calls on separate feature requests.