wanted: framework for creating nice step by step graphical visualisations of running Python code

[Claudio Grondi]

Today I bumped by chance into explaining what algorithms do by using 
animation (Java applets):
   http://www-sr.informatik.uni-tuebingen.de/~buehler/BM/BM1.html

Is there any tool in Python (except pyGame, Tkinter or other general 
purpose visualization tools) I am not aware of which would make it easy 
to create a similar, animated run through Python script code?

A free debugging tool capable of stepping line by line through Python 
code showing values of selected objects will do as a first approach, but 
it would be nice to be able to output also some graphics and/or text 
like it is done in the mentioned above example at pre-defined points in 
code called there
   /* visualisation step */

Any hints towards getting or constructing such a framework are welcome.

Claudio Grondi