Thanks for the tips, it was the missing wrapper. I'm quite a newbie in Python programming, so please forgive me. I've got two other questions: 1. Say we have a Class A with an attribute myObjects which is just a list. Now, I'd like to write my own Class B(A) - it extends A. But, in Class B, myObjects has to be a method because it has to be rebuild everytime it is called. So, how can I do something like: myObjects = getMyObjects() ? I tried to do this in the class itself, didn't work. Also tried self.myObjects = self.getMyObjects() - result wasn't what I wanted, myObjects got (of course) the resulting list of getMyObjects(), but I need myObjects to be a reference to getMyObjects() How to do this? 2. Class A has another attribute, say data, which I want to control in Class B(A), i. e. everytime data is accessed (reading or writing), I want to intercept those actions. If it was just reading, I could use the strategy from 1., but I also want to control made changes to that attribute. Do I absolutely have to rewrite all the methods which access the wanted attribute, or is there another possibility with some kind of references, perhaps similar to software interrupts in DOS? Thanks for your patience! Lars -- Lars Heber T-Systems GEI GmbH Hausanschrift: Clausstrasse 3, 09126 Chemnitz Postanschrift: Clausstrasse 3, 09126 Chemnitz Telefon : (+49 371) 5359-271 Fax : (+49 371) 5359-133 E-Mail : Lars.Heber@t-systems.com Internet: http://www.t-systems.de