asynckivy

AsyncKivy

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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 code above 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

Pin the minor version.

poetry add asynckivy@~0.7
pip install "asynckivy>=0.7,<0.8"

Usage

import asynckivy as ak

async def some_task(button):
    # waits for 2 seconds to elapse
    dt = await ak.sleep(2)
    print(f'{dt} seconds have elapsed')

    # waits for a button to be pressed
    await ak.event(button, 'on_press')

    # waits for the value of 'button.x' to change
    __, x = await ak.event(button, 'x')
    print(f'button.x is now {x}')

    # waits for the value of 'button.x' to become 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 for either 5 seconds to elapse or a button to be pressed.
    # i.e. waits at most 5 seconds for a button to be pressed
    tasks = await ak.wait_any(
        ak.sleep(5),
        ak.event(button, 'on_press'),
    )
    print("Timeout" if tasks[0].finished else "The button was pressed")

    # 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 for both 5 seconds to elapse and a button to be pressed.
    tasks = await ak.wait_all(
        ak.sleep(5),
        ak.event(button, 'on_press'),
    )

    # nest as you want.
    # waits for a button to be pressed, and either 5 seconds to elapse 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("5 seconds elapsed" if child_tasks[0].finished else "other_async_func has completed")

ak.start(some_task(some_button))

For more details, read the documentation.

Tested on

• CPython 3.9 + Kivy 2.3.0
• CPython 3.10 + Kivy 2.3.0
• CPython 3.11 + Kivy 2.3.0
• CPython 3.12 + Kivy 2.3.0 (3.12.0 is not supported due to this issue)

Why this even exists

Kivy supports two legitimate async libraries, asyncio and Trio, starting from version 2.0.0, so developing another one seems like reinventing the wheel. Actually, I started this one just to learn how the async/await syntax works, so it initially was "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 that by running investigation/why_xxx_is_not_suitable_for_handling_touch_events.py, and mashing a mouse button as quickly as possible. 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 touch handling in Kivy. (If you fail to handle touches promptly, their state might undergo changes, leaving no time to wait for tasks to resume/start). 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.