[Zope] what am i doing wrong?

Hi all! What am i doing wrong if newObject = context.manage_addProduct['myProduct'].someClass.createInObjectManager (id = 'test', context.REQUEST) works fine and zclass = someClass newObject = context.manage_addProduct['myProduct'][zclass].createInObjectManager (id = 'test', context.REQUEST) raises an Attribute Error? Thank you very much! Markus