[Tkinter-discuss] Can't do proper event binding in a for loop

[Michael O'Donnell]

Much simpler, and closer to the original posters intention.
Replace your up_and_down function with:

def up_and_down(*buttons):

  for i in range(len(buttons)-1):
    buttons[i].bind("<Down>", lambda e, x=buttons[i+1]: x.focus_set())

  for i in range(1, len(buttons)):
    buttons[i].bind("<Up>", lambda e, x=buttons[i-1]: x.focus_set())


...basically, with this code, the "i" is being evaluated within the loop,
and passed to the lambda as the x parameter. The 'e' parameter
will be set to the event object.

Mick


On Tue, Oct 19, 2010 at 2:01 PM, thea_t <siatogia at yahoo.com> wrote:
>
> Thank you guys! I know what's wrong now! :)
>
>
>
> Michael Lange wrote:
>>
>> Hi,
>>
>> Thus spoketh Firat Ozgul <ozgulfirat at gmail.com>
>> unto us on Tue, 19 Oct 2010 13:19:03 +0300:
>>
>>> Hello,
>>>
>>> for loop doesn't work, because in a for loop all events will be bound
>>> all at once, and you will only see the effect of the last binding. You
>>> need something that binds events one by one.
>>>
>>> If I were you, I would use the next() method of Python iterators:
>>
>> I think the OP suffered from a different problem in her code, namely the
>> IndexError that will be raised when i+1 or i-1 become >2 or <0 .
>> I guess what she wanted to achieve can be done, but not with this simple
>> lambda, she needs to catch the IndexError with something like:
>>
>> def up_and_down(*buttons):
>>
>>     def callback(event):
>>         index = list(buttons).index(event.widget)
>>         try:
>>             if event.keysym == 'Up':
>>                 buttons[index - 1].focus_set()
>>             elif event.keysym == 'Down':
>>                 buttons[index + 1].focus_set()
>>         except IndexError:
>>             pass
>>
>>     for i in range(len(buttons)-1):
>>         buttons[i].bind("<Down>", callback)
>>
>>     for i in range(1, len(buttons)):
>>         buttons[i].bind("<Up>", callback)
>>
>> I hope this helps
>>
>> Michael
>>
>> .-.. .. ...- .   .-.. --- -. --.   .- -. -..   .--. .-. --- ... .--. . .-.
>>
>> Wait!  You have not been prepared!
>>               -- Mr. Atoz, "Tomorrow is Yesterday", stardate 3113.2
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>
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