[Tkinter-discuss] tkinter "monitor" and root.mainloop()

[Peter Milliken]

True, sleep() pauses the main app - if you run it there. It wasn't obvious
to me from the original question that this might be a problem :-)

In my application (a simple egg timer that allows on the fly creation of new
timers and allows timing in relative or absolute terms i.e. in 5 minutes 23
seconds alert me or at 10:06:55 alert me) I leave the sleep() call down in
the thread that I created for each timer - so each "timer" thread pauses for
X seconds (1 second in my case because that is the smallest increment of
time that I am interested in).

I use Pmw for all my GUI work - after getting your mind around how flexible
it can be, you can create some amazingly power applications that can
reconfigure themselves on the fly for the user - one of the best programming
interfaces I have ever used! The guy who did this has my complete
admiration! :-)

Perhaps (just for fun :-)) think about recreating your application using
threads and (message) queues to pass information between the main Tk loop
and the various threads that you create.

Be careful - Tkinter in not re-entrant and you need to leave all of your
graphics manipulations in the mainloop - but you can safely do all sorts of
other stuff (checking files for changes etc etc) in threads - as long as
they don't do any GUI work then you are safe.

Doing threaded applications in Tk is definitely not for the beginner - you
can find cookbook examples of using threading with Tk.

Personally I find it kind of fun to do - I work in real-time embedded
systems programming, so threading and tasking is very familiar territory.
But if you ever want to expand your horizons give it some thought - but be
mindful that it requires a different mindset to that of straight "linear"
thinking programming - many programmers have some difficulty when they are
first exposed to threads and multi-tasking applications - but once you get
past that barrier you start to think in those terms with ease :-)

Peter

On Mon, May 26, 2008 at 6:00 AM, Cameron Laird <Cameron at phaseit.net> wrote:

> On Fri, May 23, 2008 at 02:52:44PM +0000, Cameron Laird wrote:
> >                       .
> >                       .
> >                       .
> > > and thanks for the answers: how, i avoided the sleep() approach,
> > > because, as Cameron said i supposed that it freezed the application:
> > > being in sleep() it stops the mainloop()...
> > >
> > > Now,
> > >
> > > i have used the after() approach, with some satisfactory results,
> > > only, there is something that still bugs me: if i understand correctly
> > > after() tells the loop to execute someething after some time (in
> > > milliseconds). What i'd like to do is something more like every()...
> > > In fact, i'd like the application to be redrawn every() second (so to
> > > say), while, if i understand correctly, every time i want to redraw
> > > the application (for example because in the meantime the log i'm
> > > monitoring has changed) i have to call after(). In this sense i have
> > > put an after() at the end of every possible event that the user, while
> > > working on the interface, could do. But, if nothing happens at the GUI
> > > level, then nothing is updated.
> > >
> > > I'd prefer to avoid to put a "UPDATE" button on the app, but as of
> > > now, seems like it's the only way to do it safely.
> > >
> > > I am wrong?
> >                       .
> >                       .
> >                       .
> > Yes and no.
> >
> > every() is a common need among Tkinter() programmers,
> > for all the reasons you describe.  I'm sure several
> > of us have written our own version, but, to my
> > surprise--astonishment!--I can't put my hands on one
> > of them in public space just now.
> >
> > I'm late for a meeting myself; I'll summarize:
> > A.  You do NOT need to have after()s all
> >     over the widget tree, although I can
> >     understand the confusion;
> > B.  All that's necessary is a single
> >     "free-running" after() *that
> >     invokes itself*; and
> > C.  After I get out of my meetings, I'll
> >     write an example.
>                         .
>                        .
>                        .
> I need to put this minimal example of after()-based polling in the Wiki ...
>
>  import Tkinter
>  import time
>
>  root = Tkinter.Tk()
>
>  def my_update():
>      display.set("The time now is '%s'." % time.asctime(time.localtime()))
>          # Re-invoke myself in two seconds.
>      root.after(2000, my_update)
>
>  display = Tkinter.StringVar()
>  window = Tkinter.Label(root, textvariable = display)
>  window.pack()
>  my_update()
>  root.mainloop()
>
> The effect is to create a textual clock which updates every two seconds,
> while keeping the window "live".
> _______________________________________________
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> Tkinter-discuss at python.org
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>
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