code: def make(base_classes=(), have_mt=False):
          
  
          good_bc = ModelFactory.__fix_bases(base_classes, have_mt)
          print "Base classes are:", good_bc
          key = "".join(map(str, good_bc))
          if key in ModelFactory.__memoized:
              return ModelFactory.__memoized[key]
  
          cls = new.classobj('', good_bc, {'__module__': '__main__', '__doc__': None})
          ModelFactory.__memoized[key] = cls
          return cls
docs: Use this static method to build a model class that
          possibly derives from other classes. If have_mt is True,
          then returned class will take into account multi-threading
          issues when dealing with observable properties.