text: Title: Screen flashes at each step
  Body: This has always been an issue for me.  Each time I step through a line of code, the screen flashes. If the line takes a long time to complete, all I can see is my original prompt (bash or IPython or whatever).  This is annoying when stepping through code, because the flashing is disorienting, and it's also annoying when executing a long line of code, because I can no longer see what is executing until it is done.  This also happens a lot if there are print statements, as the statement is printed at the "original prompt".
  
  Is this easily fixable, or is it an Urwid issue?  I haven't looked at the code yet, but maybe just the screen redrawing commands need to be reorganized a little bit.  Can you also reproduce this?
  