Changing global variables in tkinter/pmw callback

[Carey Evans]

Brian Elmegaard <be at mek.dtu.dk> writes:

> I never found out how to pass arguments to a tkinter callback without
> using a lambda.

Usually you pass a bound method, or an instance of a class with a
__call__ method.  For the latter, my brother uses something like this:

    class Command:
        def __init__(self, func, *args, **kw):
            self.func = func
            self.args = args
            self.kw = kw

        def __call__(self, *args, *kw):
            args = self.args + args
            kw.update(self.kw)
            self.func(*args, **kw)

So if you have a function "on_click" that you want to pass a
particular variable to, you do something like:

    def on_click(source, counter=None, button=None):
        print "%s from %s clicked." % (button, source)
        counter[0] += 1

    def setup():
        button = Button()
        count = [0]
        button.configure(command=Command(on_click, 'setup', counter=count))

A more Pythonic way would be to use a separate class, and pass a bound
method:

    class ButtonClicker:
        def __init__(self, source, button):
            self.source = source
            self.button = button
            self.count = 0

        def on_click(self):
            print "%s from %s clicked." % (self.button, self.source)
            self.count += 1

    def setup():
        button = Button()
        clicker = ButtonClicker('setup', button)
        button.configure(commmand=clicker.on_click)

-- 
	 Carey Evans  http://home.clear.net.nz/pages/c.evans/

	    "Quiet, you'll miss the humorous conclusion."