app.py

import concurrent.futures
from h2o_wave import main, app, Q, ui
import boto3
import asyncio


def download(q: Q, loop: asyncio.AbstractEventLoop):
    bucket = 'h2o-wave'
    file_key = 'releases/h2o_wave-0.22.0-py3-none-win_amd64.whl'
    # Get the total size of the file.
    total = boto3.client('s3').head_object(Bucket=bucket, Key=file_key)['ContentLength']
    already_downloaded = 0

    # Nested update function that is called periodically from within boto.
    def update(val):
        nonlocal already_downloaded
        already_downloaded += val
        # Update the Wave UI.
        asyncio.ensure_future(update_ui(q, already_downloaded / total), loop=loop)

    # Since boto3 is synchronous, this download is blocking.
    boto3.resource('s3').Bucket(bucket).download_file(
        file_key, 'hello.whl', Callback=update
    )
    asyncio.ensure_future(show_notification(q), loop=loop)

async def show_notification(q: Q):
    q.page['meta'].dialog = None
    q.page['meta'].notification_bar = ui.notification_bar(
        name='success_notification',
        text='Job done!',
        type='success',
        events=['dismissed']
    )
    await q.page.save()

async def update_ui(q: Q, value: int):
    q.page['meta'].dialog.items[0].progress.value = value
    await q.page.save()

@app('/')
async def serve(q: Q):
    # Unimportant, draw initial UI.
    if not q.client.initialized:
        q.page['meta'] = ui.meta_card(box='')
        q.page['form'] = ui.form_card(box='1 1 2 1', items=[
            ui.button(name='start_job', label='S3 download'),
        ])
        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),
        ])

        # Get the current event loop to update UI later.
        loop = asyncio.get_event_loop()
        with concurrent.futures.ThreadPoolExecutor() as pool:
            await q.exec(pool, download, q, loop)

    # 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()