The keys, values and items methods of dict_proxy return a list, while dict.keys, etc. return dictionary views (dict_keys, etc.). dict_proxy is used as the __dict__ attribute of classes. This is documented at http://docs.python.org/dev/py3k/reference/datamodel.html under "Custom classes" as "Special attributes: ... __dict__ is the dictionary containing the class’s namespace ..." While __dict__ is not actually dict, it probably should behave like a dict as close as possible. For example set operations work for dict.keys(), but not for dict_proxy.keys().