Button on_click with async function that takes additional arguments

Panel
1

I need to asyncify a function that I have that takes two positional arguments when applying it in the button.on_click() method. How can I enhance the code found in the documentation?


import panel as pn
pn.extension()

button1 = pn.widgets.Button(name='Click me!')
button2 = pn.widgets.Button(name='Click me too!')

text = pn.widgets.StaticText()

def run(arg1, arg2):
    text.value = f'Running {event.new}'
    text.value = f'Finished {event.new}'

button1.on_click(lambda event: run('hi', 'hello')
button2.on_click(lambda event: run('bye', 'goodbye')

The way I want to do it would look oddly like this, but I’m sure there’s an error somewhere. I need to asyncify the run method. How do I do it?

2

maybe

from itertools import partial
partial(run, arg2="hello")
3

does it make it asynchronous?

4

No, you have to make run async

5

You can use partial as shown below.

import panel as pn
from functools import partial
from asyncio import sleep

pn.extension()

button1 = pn.widgets.Button(name='Click me!')
button2 = pn.widgets.Button(name='Click me too!')

text = pn.widgets.StaticText()

async def run(event, arg1, arg2):
    text.value = f'Running {event.new} {arg1} {arg2}'
    await sleep(1)
    text.value = f'Finished {event.new} {arg1} {arg2}'

button1.on_click(partial(run,arg1='hi', arg2='hello'))
button2.on_click(partial(run,arg1='bye', arg2='goodbye'))

pn.Column(
    text, button1, button2
).servable()

Alternative pn.bind

You can also use pn.bind instead of partial

import panel as pn
from functools import partial
from asyncio import sleep

pn.extension()

button1 = pn.widgets.Button(name='Click me!')
button2 = pn.widgets.Button(name='Click me too!')

text = pn.widgets.StaticText()

async def run(event, arg1, arg2):
    text.value = f'Running {event.new} {arg1} {arg2}'
    await sleep(1)
    text.value = f'Finished {event.new} {arg1} {arg2}'

button1.on_click(pn.bind(run,arg1='hi', arg2='hello'))
button2.on_click(pn.bind(run,arg1='bye', arg2='goodbye'))

pn.Column(
    text, button1, button2
).servable()
2 Likes
6

Thanks for the solution, it worked both - using pn.bind and partial functions. I decided to go with the second option. However, it became buggy when I added --num-threads=0 to my service. What possibly could have made it wrong?

The error is found here: Serialization Problem is more frequent with thread pooling

After some digging, I realized that it lands on the “run” method that you shared, however, inconsistently hitting different line of code every time. I can safely assume that the issue is not with code, but rather the code with thread pooling.

7

Are you able to reproduce it with Marc’s pn.bind code? If so, you can report it on GitHub