app.py

import asyncio
from h2o_wave import main, app, Q, ui


async def polling_function(q: Q):
    count = 0
    total = 10
    while count < total:
        # You would make an async HTTP call here in real-world to get the fresh data.
        await q.sleep(1)
        count +=1
        q.page['meta'].dialog.items[0].progress.value = count / total
        await q.page.save()
    

@app('/')
async def serve(q: Q):
    # Unimportat, draw initial UI.
    if not q.client.initialized:
        q.page['meta'] = ui.meta_card(box='')
        q.page['form'] = ui.form_card(box='1 1 1 1', items=[
            ui.button(name='start_job', label='Start job'),
        ])
        q.client.initialized = True
    
    # Handle start job button click.
    if q.args.start_job:
        q.page['meta'].dialog = ui.dialog(title='Blocking job', blocking=True, items=[
            ui.progress(label='Progress', value=0),
            ui.button(name='cancel', label='Cancel'),
        ])
        # Start the polling, wrap in future so that we can cancel it later.
        q.client.future = asyncio.ensure_future(polling_function(q))
        # Future cancellation raises an error - use trycatch.
        try:
            # Wait until polling finished.
            await q.client.future
            q.page['meta'].dialog = None
            q.page['meta'].notification_bar = ui.notification_bar(
                name='success_notification',
                text='Job done!',
                type='success',
                events=['dismissed']
            )
        # Handle cancellation.
        except asyncio.CancelledError:
            q.page['meta'].dialog.items[0].progress.caption = 'Cancelled'

    if q.args.cancel:
        q.client.future.cancel()
    
    # Unimportant, just handle notification dismissal.
    if q.events.success_notification and q.events.success_notification.dismissed:
        q.page['meta'].notification_bar = None

    await q.page.save()