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

[thea_t]

Very clever! Thanks!


Mick O'Donnell wrote:
> 
> 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
>>>
>>> .-.. .. ...- .   .-.. --- -. --.   .- -. -..   .--. .-. --- ... .--. .
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>>>
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>>
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