Use Asynchronous Processing

When using Python you can use async callbacks wherever you would ordinarily use a regular synchronous function. For instance you can use pn.bind on an async function:

import aiohttp
import panel as pn

widget = pn.widgets.IntSlider(start=0, end=10)

async def get_img(index):
    url = f"https://picsum.photos/800/300?image={index}"
    if pn.state._is_pyodide:
        from pyodide.http import pyfetch
        return pn.pane.JPG(await (await pyfetch(url)).bytes())

    import aiohttp
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            return pn.pane.JPG(await resp.read())

pn.Column(widget, pn.bind(get_img, widget))

In this example Panel will invoke the function and update the output when the function returns while leaving the process unblocked for the duration of the aiohttp request.

Similarly you can attach asynchronous callbacks using .param.watch:

widget = pn.widgets.IntSlider(start=0, end=10)

image = pn.pane.JPG()

async def update_img(event):
    url = f"https://picsum.photos/800/300?image={event.new}"
    if pn.state._is_pyodide:
        from pyodide.http import pyfetch
        image.object = await (await pyfetch(url)).bytes()
        return

    import aiohttp
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            image.object = await resp.read()

widget.param.watch(update_img, 'value')
widget.param.trigger('value')

pn.Column(widget, image)

In this example Param will await the asynchronous function and the image will be updated when the request completes.