http://abyssly.com/2013/08/19/python_types_and_objects/
http://www.cafepy.com/article/python_types_and_objects/python_types_and_objects.html#before-you-begin
http://abyssly.com/2013/08/19/python_attributes_and_methods/
原文：http://www.cnblogs.com/stemon/p/4995403.html