[Tutor] (no subject)

[Daniel Yoo]

On Wed, 11 Apr 2001, Glen Bunting wrote:

> Your version works perfectly except for one thing, when I click on the quit
> button, nothing happens.  I will continue to use the program the way you
> wrote it, but I have a few questions about the way I was trying to write it.

Hmmm... strange!  What might be happening is that the updating action is
taking a long time.  At the moment, the program is written to only be able
to do one task at a time.  The call to:

     urllib.urlretrieve('http://www.esynch.com/mw_test.dat', 'test')

takes a heck of a lot of time, precisely because the file is HUGE, even
with a broadband connection.  *grin*.  That's probably why the GUI isn't
as responsive as it should be: it's only doing one thing at a time.  Try
your program on a less stressful URL, and see if this is the case.


> 2:  As long as Tkinter.mainloop() remains in the while loop, the while
> loop does not continue until after I quit Tkinter.  Once I do that the
> loop continues.  If I take Tkinter.mainloop out of the while loop, the
> loop continues like it should , but the gui never pops up.

The role of the mainloop() call is to pass control of your program off to
Tkinter --- after caling mainloop(), it's all "hands-off".  I believe this
is called "event-driven programming", because anything that happens
afterwards is a response to what the user does with the GUI.


The control flow of our GUI programs, then, looks like:

start  ----> initialize stuff ---> initialize GUI -+
                                                   |
            +------------------<-------------------+
            |
            +----> do GUI stuff ---+---> turn off GUI ---> done!
            |                      |
            +----------<-----------+
                handle an "event"


The "do GUI stuff" loopiness is what the mainloop() is doing: it keeps on
looping until we can't look at any more "events", and then we finish the
program.  It's a different style of programming than what you might be
used to.


> The next thing I might be interested in doing is to graph the results.  Is
> that the next logical step, or would that be a little to advanced for a
> newbie?

Graphing sounds like a great idea.  You'll want to play around with the
Canvas widget.  If you want, I can take a look at Grayson's "Python and
Tkinter Programming" to review how Canvases work.

There's supposedly a really good module that works with Tkinter to make
really nice widgets.  It's called Python Mega Widgets, and I think it has
a graphing widget that might be useful.  If you're interested, take a
look:

    http://pmw.sourceforge.net

Lots of good stuff.


Anyway, good luck to you.