Configuration Files and Tkinter--Possible?

[W. eWatson]

Gabriel Genellina wrote:
> En Wed, 04 Mar 2009 12:12:50 -0200, W. eWatson <notvalid2 at sbcglobal.net> 
> escribió:
> 
>> That's fine, but I think my problem boils down to one question. There 
>> seem to be two ways to communicate with a dialog (I mean a collection 
>> of widgets assembled in a window that requires the user enter various 
>> parameters, integers, strings, yes/no button, etc.): 1. a callback and 
>> 2. control variables. Which one should be used?
> 
> The simplest way that probably works. The one you feel most comfortable 
> with. The one best fits your application. There is no single answer.
> 
>> To be more explicit, look at this code from your source above 
>> <http://effbot.org/tkinterbook/entry.htm>. (This is about the simplest 
>> "dialog" one can have.) :
> [...code...]
>> Note that above this example, the author mentions:
>> "You can also bind the entry widget to a StringVar instance, and set 
>> or get the entry text via that variable:
>> Why have two ways of doing this?
> 
> You may have some related widgets, and want to keep them syncronized. By 
> example, a slider 0-100 and a text entry for some percentage. Moving the 
> slider changes the number displayed, and editing the number moves the 
> slider accordingly. There are other ways of doing the same: you may 
> react to some events in one widget, and alter the other accordingly. But:
> - that requires that you know *which* events actually modify the value
> - increases coupling between all your widgets (consider what happens 
> when you want to add an image showing the effect of moving the slider)
> 
> So, in some cases, it is more convenient to use bound variables. You may 
> consider this as a micro-application of the Model-View-Controller pattern.
> 
> That said, I seldom use bound variables (but I seldom write GUIs using 
> Tkinter either).
> 
Thanks, unfortunately I have no choice. I'm modifying a program that uses 
Tkinter, and so not to take on extra work, I need to stick with Tkinter. The 
author, for some reason, found it useful to use control variables.

In trying to add a configuration file to the code, the control variables 
make it difficult. I have already coded the config file reading, writing, 
and setting of variables (setattr came in very handy to get the fixed code 
out of the way). However, to set them in the main dialog, is not easy, 
because it uses code like self.colorVar = IntVar() and 
dialog.colorVar.get(). To get rid of this written (hard) code, I have to 
manufacture it somehow by forming it from the names found in the config 
file, e.g., color=1. I'm aware of eval and exec, but wary of their use. It 
seems like the solution to all this is not to use control variables, if 
possible. Presently, I have no idea whether it is absolutely needed for the 
program.

 From what I can see on the web, and the few texts I have had access to, no 
one makes a clear distinction between the two choices by way of words or 
examples. This comes close:

 From Tkinter reference: a GUI for Python
One special quality of a control variable is that it can be shared by a 
number of different widgets, and the control variable can remember all the 
widgets that are currently sharing it. This means, in particular, that if 
your program stores a value v into a control variable c with its c.set(v) 
method, any widgets that are linked to that control variable are 
automatically updated on the screen.

I'm just getting into Tkinter, so that doesn't quite do it for me.

I originally mentioned, " ... it seems as though someone should have had a 
similar problem in the past." What I meant was implementing a config file 
arrangement with Tkinter. I was suggesting this seems nearly, if not, 
impossible with control variables, so there must be another way. I think the 
other way is described in the example I provided.

Well, I think it's now time to go back to the code, and see what I can do to 
get rid of the control variables.

-- 
                                W. eWatson

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