Tkinter Newbie Question

[Marc 'BlackJack' Rintsch]

On Thu, 06 Dec 2007 23:04:56 -0800, robbie wrote:

> This second example doesn't work.  The only difference is that I gave
> the salutation function a parameter and tried to pass a string as the
> parameter from the button. It appears to call the function once for
> each window as they're being created, but doesn't do anything when the
> buttons in the windows are pressed.
> 
> from Tkinter import *
> root = Tk()
> 
> trees = [('The Larch!',          'light blue'),
>          ('The Pine!',           'light green'),
>          ('The Giant Redwood!',  'red')]
> 
> def salutation(j=""):
>     print j + " Something!"
> 
> for (tree, color) in trees:
>     win = Toplevel(root)
>     win.title('Sing...')
>     win.protocol('WM_DELETE_WINDOW', lambda:0)
>     win.iconbitmap('py-blue-trans-out.ico')
>     msg = Button(win, text='Write Something',
> command=salutation(tree))

You are calling the function here.  Parenthesis after a callable like a
function means "call it *now*", so you are calling `salutation()` and bind
the *result* of that call to `command`.  An idiomatic solution is to use a
``lambda`` function::

    msg = Button(win,
                 text='Write Something',
                 command=lambda t=tree: salutation(t))

In Python 2.5 there's an alternative way with the `functools.partial()`
function:

from functools import partial

# ...

    msg = Button(win,
                 text='Write Something',
                 command=partial(salutation, tree))

Ciao,
	Marc 'BlackJack' Rintsch