[Tutor] help with Tkinter, please

[Dick Moores]

At 08:55 PM 11/26/2006, you wrote:
>On 27/11/06, Dick Moores <rdm at rcblue.com> wrote:
>>I have a question about the "EXIT" button's command,
>>command=sys.exit. It fails to quit the program when I've entered too
>>large an integer for factoring, or for prime testing, and I don't
>>want to wait any more for the result. When I'm running the program
>>from my Win XP console, I can quit with a simple Ctrl+C, but this
>>won't be available to the friend I may send the executable to. Is it
>>possible to build in a way to smoothly interrupt, say, a factoring
>>process that's taking too long?
>
>Well, as you may know, the "core" of Tkinter (or most GUIs, I think)
>is the event loop.  The event loop basically does this:
>1. Look for events (mouse clicks, keypresses, etc.)
>2. Process events (update widgets, call callbacks)
>3. GOTO 1.
>
>So, in this specific case, the event loop is doing this:
>
>1. Look for events ==> user clicks on "factorise" button.
>2. Process events ==> call "factorise" button callback.
>3. Callback runs...
>4. ...callback completes.
>5. Look for events ==> user clicks on "exit" button.
>6. Process events ==> call "exit" button callback.
>7. Python exits.
>
>So, you can see why clicking your exit button won't interrupt the
>calculation in progress.  The only way you can do that is if you can
>get the event loop to start looking for events again before the
>callback finishes.  And that means THREADS.

Thanks, John. I know nothing about threading. I see that Chun's _Core 
Python Programming_, 2nd ed. has a 30-page chapter on it. A good 
place to start?

Dick