Dustan wrote:
> Jay wrote:
>
>>Thanks for the tip, but that breaks things later for what I'm doing.
>>
>>[EMAIL PROTECTED] wrote:
>>
>>>In that case you don't need a lambda:
>>>
>>>import Tkinter as tk
>>>
>>>class Test:
>>> def __init__(self, parent):
>>> buttons = [tk.Button(parent, text=str(x+1),
>>>command=self.highlight(x)) for x in range(5)]
>>> for button in buttons:
>>> button.pack(side=tk.LEFT)
>
>
> Well, actually, that's wrong. You obviously don't understand why lambda
> is necessary for event binding; in this case (and many others, for that
> matter), the button gets bound to the event *returned* by
> self.highlight(x), which, since nothing gets returned, would be None.
> Then when you click the button, Tkinter calls None(), and out of the
> blue, an error is raised.
>
> Lambda is the safe way around that error.
>
>
>>> def highlight(self, x):
>>> print "highlight", x
>>>
>>>root = tk.Tk()
>>>d = Test(root)
>>>root.mainloop()
>>>
>>>Bye,
>>>bearophile
>
>
Actually, lambda is not necessary for event binding, but a closure (if I
have the vocab correct), is:
import Tkinter as tk
def make_it(x):
def highliter(x=x):
print "highlight", x
return highliter
class Test:
def __init__(self, parent):
buttons = [tk.Button(parent, text=str(x+1),
command=make_it(x)) for x in range(5)]
for button in buttons:
button.pack(side=tk.LEFT)
root = tk.Tk()
d = Test(root)
root.mainloop()
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com/
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