[Tutor] Help me understand this tkinter related code

[Alan Gauld]

Please don't hijack an old message to create a new subject.
Those of us using threaded readers might not see it and you
lose potential answers.


"Robert DeLaurentis" <lists at bobdel.com> wrote

> The local function change_volume(v) requires the argument v to operate 
> properly,
> but I'm unclear where the value of that argument is being set or why the 
> code fails
> without it.

> def change_volume(v):
>    track.set_volume(volume.get())
>
> volume_scale = Scale(app,
>                        variable     = volume,
>                        from_        = 0.0,
>                        to           = 1.0,
>                        resolution   = 0.1,
>                        command      = change_volume,
>                        label        = "Volume",
>                        orient       = HORIZONTAL)

I'm not familiar with the wodget in question but it looks like the command 
callback
expects to pass a parameter to the callback function. Therefore the 
function needs
to provide a placeholder even though it doesn't use it!

You would need to find the documentation for the widget to confirm that 
theory
however.

A Google seartch threw up this:

http://infohost.nmt.edu/tcc/help/pubs/tkinter/scale.html

Which seems to confirm my theory :-)


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/