How do I add a callback with arguments to a button?

Panel
1

Hi, I’m trying to do something conceptually very simple, but somehow still failing to figure it out. I just want to be able to call a function with some arguments when I click a button.

def add_data(event, some_data, list_of_data):
	print(event)
	list_of_data.append(some_data)

def main():
	validationButton = pn.widgets.Button(name='Validate', button_type='primary')
	validationButton.on_click(add_data)

Obviously, this doesn’t work, as I’m not providing some_data and list_of_data to add_data(), but I can’t find a way to do so that actually works.

If I remove these two arguments from add_data() and only leave event as an argument, this executes as expected. I tried messing around with binding or decorators, but with no success. The only thing that does work is to make some_data and list_of_data global variables, but there must be a way to do this in a cleaner fashion.

Any advice?

2

You should be able to achieve the desired result using functools.partial

from functools import partial

def add_data(event, some_data, list_of_data):
	print(event)
	list_of_data.append(some_data)

def main():
	validationButton = pn.widgets.Button(name='Validate', button_type='primary')
        some_data = "something"
        list_of_data = []
	validationButton.on_click(partial(add_data, some_data, list_of_data))
2 Likes
3

Indeed! It seems the problem wasn’t my lack of Panel expertise as much as my lack of Python expertise, in this case. Thank you very much!

Just one minor thing: it appears that doing this ends up putting the event argument last when calling add_data(), so its prototype must be modified accordingly:

from functools import partial

def add_data(some_data, list_of_data, event):
	print(event)
	list_of_data.append(some_data)

def main():
	validationButton = pn.widgets.Button(name='Validate', button_type='primary')
        some_data = "something"
        list_of_data = []
	validationButton.on_click(partial(add_data, some_data, list_of_data))
1 Like