[Stephan Herschel]

... The class looks like this:

class x: def y (s): return 1

Within Zope I now try to call the method y() of the object that is returned by the external function. This does not work - zope want's me to (re)login immediately.

I guess I'm just not allowed to use classes defined outside of zope within zope. Is there some way to register a class so that it's objects can be used inside of Zope? If so, how can I achieve this?

External methods are functions, not methods. But if the function returns an object you should be able to use its methods. You better show us just how you are trying to do this. Cheers, Tom P