Tk only processes changes to widgets when it is in control (rather than your methods). What you need to do is to pause your program and let Tk's event loop clear up its backlog; this includes redisplays.

See the Tk::Widget docs for information about the methods idletasks and update. idletasks causes "most" updates to occur; the manual states it doesn't run updates "triggered by window size changes", but it sounds like it will be sufficient for your purposes. update causes Tk to clear its desk; it handles everything, including any pending user input.

Try calling idletasks (on the main window widget, say) after you finish informing Tk of all the updates you want to take place. Failing that, try calling update instead.