Python3.6 tkinter bug?

[Christian Gollwitzer]

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)

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

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.


	Christian