What is the cleanest way to deal with on_change callbacks that do not use the arguments?

More a style question. I have a lot of places where I use the on_change handle to trigger a callback. Often I do not even use information on what exactly changed.

Bokeh however requires the exact signature of three arguments. E.g. *args is not allowed:
ValueError: Callback functions must have signature func(attr, old, new), got func(*args)

an option here would be
def callback(attr, old, new):

but these are never used, to indicate that they are not used I could do
def callback(_, __, ___)

but this may perhaps not be better.

What would be in your opinion the cleanest way of dealing with the above?

I would normally do:

def callback(_attr, _old, _new):

to indicate that the parameters aren’t used, but when someone comes to modify the function in future they can see what parameters are available to them should they need them.

Thanks, that is a good solution.