I have further information on my problem of unpickling an object that is based on Numeric.UserArray class. I can recreate the endless getattr loop with the following code, which is a small subsection of my class: data = Numeric.ones(31,savespace=1) ua = UserArray(data) blob = cPickle.dumps(ua) obj = cPickle.loads(blob) <-- fails here If you pickle the data obj, everything works. This code works in Python2.2. Is this a bug? Is it fixable? sue