app.py

async def polling_function(q: Q):
    count = 0
    total = 20
    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()