from cStringIO import StringIO
import cPickle

class A(object): pass

def fg(module, clsname):
    print 'Finding %s.%s' % (module, clsname)
    return A

pickled = cPickle.dumps(A(), 2)
up = cPickle.Unpickler(StringIO(pickled))
up.find_global = fg
up.load()