From the website: However, due to the special nature of python's builtin datatypes (str, list, int, float, tuple, dict, etc.), you will not be able to use

From the website: However, due to the special nature of python's builtin datatypes (str, list, int, float, tuple, dict, etc.), you will not be able to use chained_class on those classes. This helps to make my point about ruby's object model. Of course, ruby takes a speed hit for it, but it is more consistent in this regard.