pn.state.add_periodic_callback does not support async functions

[MarcSkovMadsen]

Panel: 0.12.1.

I've created this on the back of Discourse - Running async periodic callback

According to Panel - Async Functions, pn.state.add_periodic_callback can run async functions.

But if I try I get

C:\Users\masma\Anaconda3\envs\aw-lib\lib\site-packages\panel\io\callbacks.py:72: RuntimeWarning: coroutine 'test' was never awaited   
  self.callback()

import panel as pn
import asyncio
pn.extension()

text = pn.widgets.StaticText(value="test")

async def test():
    print("halo")
    text.value = "halo"
    await asyncio.sleep(1)
    text.value = "halo2"

pn.state.add_periodic_callback(test, period=2000)
pn.Row(text).servable()

Workaround

According to tornadoweb/tornado#2828 (comment) I should use

pn.state.add_periodic_callback(lambda: asyncio.create_task(test()), period=2000)

async.mp4

import panel as pn
import asyncio
import datetime
pn.extension()

text = pn.widgets.StaticText(value="")

async def test():
    text.value = str(datetime.datetime.now()) + " start"
    await asyncio.sleep(1)
    text.value = str(datetime.datetime.now()) + " finish"

pn.state.add_periodic_callback(lambda: asyncio.create_task(test()), period=2000)
pn.Row(text).servable()

Solution

• Maybe support async directly without the workaround
• Document with a concrete example how to schedule async periodic callbacks.