Ok, it was the import problem! Thanks to all! Q1: So, in python you've to say which class you want to import? Q2: And from test.parent.mylib means go to the directory test then parent and then use the mylib library? However, now I stumbeld on more problems. I receive an error about using an onbound method... Q3: What is an unbound method?? Thanks to another email, I could solve this 'unbound method-error' with the following line : CatalogAware.manage_afterAdd.im_func(self,item,container) Now, adding an instance works without a problem, but when a try to cut and paste the instance, I get the following message: Zope Error Zope has encountered an error while publishing this resource. Error Type: AttributeError Error Value: aq_acquire Q4: Euhm, what does this error means? Thanks, Tom.