[Zope] Problem with Python Script in RAM Cache

I wanted to cache a Python script in the ZOPE ram cache manager, but it did not work. I did hear that "RAM cache manager can only cache picklable objects". I do not understand, what that means. I heard that a dictionary would be a "picklable" object. My script returns a sequence (actually the results from a search in the PLONE catalog by the searchresults method). Does that mean, I would have to change my python script so that it would return a dictionary instead of a sequence to be able to be cached by a ram cache manager? Can anybody help me? Thanks Peter Baeuerle