PyScript asyncio porting

August 14, 2026 · View on GitHub

Who: You want an existing pydevices-examples example to run in the browser via PyScript.

Prerequisites: PyScript local setup. Read Events concept first.

Why asyncio?

PyScript's runtime is asyncio-based. A typical MCU example:

def main():
    while True:
        for event in runtime.poll():
            handle(event)
        display.show()

main()

This blocks the browser event loop. PyScript needs async def, await, and yields to the scheduler.

Port pattern

from board_config import display_drv
from app_runtime import runtime
import multimer

async def main():
    while True:
        for event in runtime.poll():
            ...  # handle event
        display_drv.show()
        await multimer.sleep_ms(0)  # yield to the event loop

runtime.run_async(main)

Prefer subscribe + keep-alive when you do not need a custom async main:

runtime.on(runtime.events.MOUSEBUTTONDOWN, handle)
runtime.run_forever()

Runtime polling

If runtime.poll() is synchronous, call it inside the async loop and await a yield each iteration so touch redraw and timers run. Use await multimer.sleep_ms(0) — no need to import asyncio.

For periodic callbacks, use multimer.AsyncTimer inside async def main() after the loop is running.

Examples to study

Script	What to copy
`calc_graphics.py`	Full async UI loop
`eventsys_simpletest.py`	Minimal poll + await
`paint.py`	Touch drawing with asyncio

Try via: .site/pyscript/micropython.html?modules=eventsys_simpletest

Minimal shell (no query string): open async.html — a bouncing square that yields with await multimer.sleep_ms(16).

Common failures

Symptom	Cause
Frozen tab	Blocking loop, no `await`
No touch response	Poll loop never yields
Import error	Example needs packages not in `micropython.toml` manifest

Regenerate manifest after adding examples: ./scripts/install_refresh_manifests.sh.

Reference

pydevices product source