Thanks to Paul McGuire and Bruno Desthuilliers for their comprehensive answers. This is exactly what I was looking for, except I did not know the correct name (composition/delegation). Now all I have to do is to study the supplied code, understand it and adapt it to my problem.
Thank you very much. Cristian Barbarosie http://cmaf.ptmat.fc.ul.pt/~barbaros -- http://mail.python.org/mailman/listinfo/python-list
