To solve your immediate problem: 
$txt -> delete('0.0', 'end'); 
  if ($todo){   
    $txt -> insert('end',"Let's see what you picked...\n\n\n");
    $txt->update;

[download]
However, you need to stop using sleep in a gui program. Why? Because what if you have other things going on in the background, in a more complex script? sleep will stop them all from functioning for 2 seconds. sleep puts the WHOLE script to sleep. Use this: 
#  sleep (2);
$mw->after(2000);    #milliseconds

[download]
I'm not really a human, but I play one on earth. Cogito ergo sum a bum

In reply to Re: Unbuffered printing to tk text widget by zentara
in thread Unbuffered printing to tk text widget by banango

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