tkinter.tix "Control" widget don't work with StringVar?

[jfong at ms4.hinet.net]

MRAB於 2019年6月2日星期日 UTC+8上午10時18分36秒寫道：
> On 2019-06-02 02:28, jfong at ms4.hinet.net wrote:
> > Below is a simplified version of the sample script downloaded from its package.
> > When run it, the entry field display '0' instead of 'P&W'.
> > PS. I am using Python 3.4.4, Windows 32bit
> > 
> > ----test0.py----
> >   1 from tkinter import tix as Tix
> >   2
> >   3 root = Tix.Tk()
> >   4
> >   5 demo_maker = Tix.StringVar()
> >   6 demo_maker.set('P&W')
> >   7
> >   8 c = Tix.Control(root, label='Engine Maker: ',
> >   9                variable=demo_maker,
> > 10                options='entry.width 10 label.width 20 label.anchor e')
> > 11 c.pack(side=Tix.TOP, anchor=Tix.W)
> > 12
> > 13 root.mainloop()
> > --------
> > 
> > I run it under pdb, try to figure out where the problem is:
> > 
> > D:\Works\Python>py -m pdb test0.py
> >> d:\works\python\test0.py(1)<module>()
> > -> from tkinter import tix as Tix
> > (Pdb) tbreak 13
> > Breakpoint 1 at d:\works\python\test0.py:13
> > (Pdb) cont
> > Deleted breakpoint 1 at d:\works\python\test0.py:13
> >> d:\works\python\test0.py(13)<module>()
> > -> root.mainloop()
> > (Pdb) !c['value']
> > '0'
> > (Pdb) !demo_maker.get()
> > 'P&W'
> > (Pdb) quit
> > 
> > If I change line 8 to "c = Tix.Control(root, label='Engine Maker: ', value='P&W',", the result is very interest:
> > 
> > D:\Works\Python>py -m pdb test0.py
> >> d:\works\python\test0.py(1)<module>()
> > -> from tkinter import tix as Tix
> > (Pdb) tbreak 13
> > Breakpoint 1 at d:\works\python\test0.py:13
> > (Pdb) cont
> > Deleted breakpoint 1 at d:\works\python\test0.py:13
> >> d:\works\python\test0.py(13)<module>()
> > -> root.mainloop()
> > (Pdb) !c['value']
> > '0'
> > (Pdb) !demo_maker.get()
> > '0'
> > (Pdb) quit
> > 
> > Anyone can help?
> > 
>  From the documentation:
> 
> """class tkinter.tix.Control
> The Control widget is also known as the SpinBox widget. The user can 
> adjust the value by pressing the two arrow buttons or by entering the 
> value directly into the entry. The new value will be checked against the 
> user-defined upper and lower limits."""
> 
> In other words, the widget that you're using is for entering a _number_; 
> you can click the up and down buttons to change its value. You usually 
> use it with tix.IntVar.
> 
> You're using it with tix.StringVar, which is for strings, and because 
> it's unable to interpret the value as a number, it's pretending that 
> it's 0 instead. You can, however, set it to, say, '1', or '01', and the 
> widget will then show the number 1.

>From the documents, it sounds that this widget was designed for number only. But the original example Control.py from https://svn.python.org/projects/stackless/trunk/Demo/tix/samples/ works on string either by changing its button command. The only thing bothers me is that why it fails at the start-up? and I can't figure out the reason:-(