asynckivy 0.6.1

Async library for Kivy

AsyncKivy

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日本語doc

asynckivy is an async library that saves you from ugly callback-style code, like most of async libraries do. Let's say you want to do:

1. print('A')
2. wait for 1sec
3. print('B')
4. wait for a button to be pressed
5. print('C')

in that order. Your code would look like this:

from kivy.clock import Clock

def what_you_want_to_do(button):
    print('A')

    def one_sec_later(__):
        print('B')
        button.bind(on_press=on_button_press)
    Clock.schedule_once(one_sec_later, 1)

    def on_button_press(button):
        button.unbind(on_press=on_button_press)
        print('C')

what_you_want_to_do(...)

It's not easy to understand. If you use asynckivy, the above code will become:

import asynckivy as ak

async def what_you_want_to_do(button):
    print('A')
    await ak.sleep(1)
    print('B')
    await ak.event(button, 'on_press')
    print('C')

ak.start(what_you_want_to_do(...))

Installation

It's recommended to pin the minor version, because if it changed, it means some important breaking changes occurred.

poetry add asynckivy@~0.6
pip install "asynckivy>=0.6,<0.7"

Usage

import asynckivy as ak

async def some_task(button):
    # waits for 1sec
    dt = await ak.sleep(1)
    print(f'{dt} seconds have passed')

    # waits until a button is pressed
    await ak.event(button, 'on_press')

    # waits until 'button.x' changes
    __, x = await ak.event(button, 'x')
    print(f'button.x is now {x}')

    # waits until 'button.x' becomes greater than 100
    if button.x <= 100:
        __, x = await ak.event(button, 'x', filter=lambda __, x: x>100)
        print(f'button.x is now {x}')

    # waits until EITHER a button is pressed OR 5sec passes.
    # i.e. wait at most 5 seconds for a button to be pressed
    tasks = await ak.wait_any(
        ak.event(button, 'on_press'),
        ak.sleep(5),
    )
    print("The button was pressed" if tasks[0].finished else "Timeout")

    # same as the above
    async with ak.move_on_after(5) as bg_task:
        await ak.event(button, 'on_press')
    print("Timeout" if bg_task.finished else "The button was pressed")

    # waits until a button is pressed AND 5sec passes.
    tasks = await ak.wait_all(
        ak.event(button, 'on_press'),
        ak.sleep(5),
    )

    # nest as you want.
    # waits for a button to be pressed AND (5sec OR 'other_async_func' to complete)
    tasks = await ak.wait_all(
        ak.event(button, 'on_press'),
        ak.wait_any(
            ak.sleep(5),
            other_async_func(),
        ),
    )
    child_tasks = tasks[1].result
    print("5sec passed" if child_tasks[0].finished else "other_async_func has completed")

ak.start(some_task(some_button))

Tested on

• CPython 3.8 + Kivy 2.2.1
• CPython 3.9 + Kivy 2.2.1
• CPython 3.10 + Kivy 2.2.1
• CPython 3.11 + Kivy 2.2.1

Why this even exists

Kivy supports two legit async libraries, asyncio and Trio, from version 2.0.0 so developing another one seems reinventing the wheel. Actually, I started this one just for learning how async/await works so it was initially "reinventing the wheel".

But after playing with Trio and Kivy for a while, I noticed that Trio is not suitable for the situation where fast reactions are required e.g. touch events. The same is true of asyncio. You can confirm it by running investigation/why_xxx_is_not_suitable_for_handling_touch_events.py, and mashing a mouse button. You'll see sometimes up is not paired with down. You'll see the coordinates aren't relative to the RelativeLayout even though the target belongs to it.

The cause of those problems is that trio.Event.set() and asyncio.Event.set() don't immediately resume the tasks waiting for the Event to be set. They just schedule the tasks to resume. Same thing can be said to nursery.start_soon() and asyncio.create_task().

Trio and asyncio are async I/O libraries after all. They probably don't have to immediately resumes/starts tasks, which I think necessary for Kivy's touch handling. (If a touch is not handled immediately, its state may change). Their core design might not be suitable for GUI in the first place. That's why I'm still developing this asynckivy library to this day.