Tkinter: Any way to flush events without blocking?

[Russell E. Owen]

In article <c9d82136.0402241037.69be029a at posting.google.com>,
 noah at noah.org (Noah) wrote:

>I have a long running application with a Tkinter GUI.
>Is there a way to see how many events are pending in the queue?
>I want my application to occasionally process events (so that the
>output window will update; the root window will refresh if
>the user moves it; etc.). 
>
>I tried using Tk.tk.dooneevent(), but it blocks if no events are
>available. What I thought of doing is calling a method that
>does something like this:
>        # event_queue_empty() does not exist
>        while not root.tk.event_queue_empty(): 
>                root.tk.dooneevent(0)

I think this is what you want:
tk_object.update_idletasks()

>The problem is that I'm calling an imported Python method 
>that runs for a long time. I can't easily retrofit it into an 
>event-oriented application.
...
>I suppose that my other option is to use a thread, but that
>seems overkill when all I want is a updated window.

update_idletasks() will do what you want.

But you might want to consider a thread anyway. This would be especially 
nice if there is any way to add code to the long-running task that would 
check to see if the user had aborted. In that case having a thread means 
you could implement a responsive "Cancel" button. As far as 
communicating from the thread to the main task, there are several 
options, including:

- Have the background thread write its output to a Queue and poll the 
Queue with an after() loop. This is dirt simple, though a bit 
inefficient.
- Have the background thread create an event. Bind a callback to that 
event. The callback will run in the main loop, so is safe for writing to 
Tk widgets. I read about this neat trick recently on this news group.

(Whatever you do, don't have the background thread try to write to Tk 
widgets or set Tk variables. But I assume you know that.)

-- Russell