Use threads or Tkinter event loop?

Kevin Walzer kw at codebykevin.com
Tue Mar 27 16:07:22 CEST 2007


Kevin Walzer wrote:
> I'm trying to decide whether I need threads in my Tkinter application or 
> not. My app is a front end to a command-line tool; it feeds commands to 
> the command-line program, then reads its output and displays it in a 
> Tkinter text widget. Some of the commands are long-running and/or return 
> thousands of lines of output.
> 
> I initially thought I needed to use threading, because the GUI would 
> block when reading the output, even when I configured the blocking to be 
> non-blocking. I got threading to work, but it seemed a bit complicated. 
> So, I decided to try something simpler, by using the Tkinter event loop 
> to force the output to update/display.
> 
> it seems to work well enough. Here is my threaded code:
> 
> non-threaded:
> 
> def insertDump(self):
>  self.finkinstalled = os.popen('/sw/bin/fink list', 'r', os.O_NONBLOCK)
>         for line in self.finkinstalled:
>             self.t.insert(END, line)
>             self.update()
>             self.t.see(END)
> 
> And here is my non-threaded code (needs two functions to work)
> 
>  def insertDump(self):
>         try:
>             data = self.dataQueue.get(block=False)
>             for line in data:
>                 self.t.insert(END, line)
>                 self.t.see(END)
>                 self.update()
> 
> 
>         except:
>             print "error"
>             raise
> 
>     def getDump(self):
> 
>         self.file = os.popen('/sw/bin/fink list', 'r', os.O_NONBLOCK)
>         self.dataQueue.put(self.file)
> 
> This brings me to a design, as opposed to coding, question. The 
> non-threaded version seems to work just as well as the threaded one, in 
> terms of speed. Moreover, it is simpler to code and debug, because I 
> don't have to check to make sure the thread queue has data (I sometimes 
> get an 'Empty' error message when I first start the thread).  Simply 
> using the Tk event loop (self.update) is also how I would have coded 
> this in Tcl.
> 
> So my question is this: under what circumstances in Python are threads 
> considered "best practice"? Am I wrong to use the Tk event loop instead 
> of threads?
> 

D'oh, I got the code snippets mixed up:

non-threaded:

def insertDump(self):
  self.finkinstalled = os.popen('/sw/bin/fink list', 'r', os.O_NONBLOCK)
         for line in self.finkinstalled:
             self.t.insert(END, line)
             self.update()
             self.t.see(END)

threaded:

  def insertDump(self):
         try:
             data = self.dataQueue.get(block=False)
             for line in data:
                 self.t.insert(END, line)
                 self.t.see(END)
                 self.update()


         except:
             print "error"
             raise

     def getDump(self):

         self.file = os.popen('/sw/bin/fink list', 'r', os.O_NONBLOCK)
         self.dataQueue.put(self.file)

Sorry!
-- 
Kevin Walzer
Code by Kevin
http://www.codebykevin.com



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