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Python3.6 tkinter bug?

Terry Reedy tjreedy at udel.edu
Wed Feb 1 06:55:11 EST 2017 
On 2/1/2017 1:37 AM, Christian Gollwitzer wrote:
> Am 01.02.17 um 00:02 schrieb MRAB:
>> On 2017-01-31 22:34, Christian Gollwitzer wrote:
>>>> .!frame.!checkbutton
>>>> .!frame.!checkbutton2
>>>> .!frame2.!checkbutton
>>>> .!frame2.!checkbutton2
>>>
>>>
>> Perhaps someone who knows Tcl and tk can tell me, but I notice that in
>> the first example, the second part of the widget names are unique,
>> whereas in the second example, the second part of the widget names are
>> the reused (both "!checkbutton" and "!checkbutton2" occur twice).
>
> It is indeed the reason, but it has some strange legacy cause: the
> default name for the checkbutton-linked variable is the name of the
> button inside the parent. Therefore creating a checkbutton has the side
> effect of creating a variable with the button's name.
>
> In this case, the first buttons in the frames are linked to a variable
> called "!checkbutton" and the other two are linked to "!checkbutton2".
> (a variable name in Tcl can be anything apart from the empty string).
> This can also be demonstrated by this Tcl script:
>
>     package require Tk
>
>     pack [frame .f1]
>     pack [frame .f2]
>
>     pack [checkbutton .f1.c1 -text "A" ]
>     pack [checkbutton .f1.c2 -text "B" ]
>
>     pack [checkbutton .f2.c1 -text "C" ]
>     pack [checkbutton .f2.c2 -text "D" ]
>
> which is equivalent to the Python code above.
>
> Note that this surprising behaviour was corrected for the (modern) ttk
> widgets, so if "checkbutton" is replaced by "ttk::checkbutton", they are
> not any longer linked. In Python, that would be
>
>     from tkinter import ttk
>     ...
>     w = ttk.Checkbutton()
>
> (Personally, I'm not using the legacy widgets any longer)

Christian, could you repeat any relevant parts of your comments on the 
tracker, especially any ideas on how we might fix tkinter?
https://bugs.python.org/issue29402

>> Do the names need to be:
>>
>> .!frame.!checkbutton
>> .!frame.!checkbutton2
>> .!frame2.!checkbutton3
>> .!frame2.!checkbutton4

Serhiy considered that but, not knowing that this would cause a 
regression, we both liked numbering within parent better.

There is a similar issue with radiobuttons on ttk.OptionMenus that 
existed *before* the 3.6 name changes.
https://bugs.python.org/issue25684
So there seems to be a systematic issue with tk or how we are (mis)using it.

> Good question. Maybe there should be unique variable names? I.e., if the
> script is changed into     package require Tk
>
>     pack [frame .f1]
>     pack [frame .f2]
>
>     pack [checkbutton .f1.c1 -text "A" -variable v1]
>     pack [checkbutton .f1.c2 -text "B" -variable v2]
>
>     pack [checkbutton .f2.c1 -text "C" -variable v3]
>     pack [checkbutton .f2.c2 -text "D" -variable v4]
>
> then they are also not linked.

-- 
Terry Jan Reedy
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