When a Tkinter window comes up that uses tkSimpleDialog to construct a 
dialog box, the window first flashes on the screen as an unpopulated 
top-level window, before being drawn in its completed state.

This problem is easily corrected by adding two lines of code to the 
constructor for class Dialog in tkSimpleDialog.py.  The first line of 
the constructor reads Toplevel.__init__( self, parent ).  After this 
line insert self.overrideredirect( True ).  The second line from the 
last in this constructor reads self.initial_focus.focus_set(), just 
before this line insert self.overrideredirect( False).  That's it.  
I've attached the revised version of this file.