let' get started with the simple case--listing attributes attached to an instance the following classcoded in the file listinstance pydefines mix-in called listinstance that overloads the __str__ method for all classes that include it in their header lines because this is coded as classlistinstance is generic tool whose formatting logic can be used for instances of any subclass client#!python file listinstance py ( xclass listinstance""mix-in class that provides formatted print(or str(of instances via inheritance of __str__ coded heredisplays instance attrs onlyself is instance of lowest class__x names avoid clashing with client' attrs ""def __attrnames(self)result 'for attr in sorted(self __dict__)result +'\ % =% \ (attrself __dict__[attr]return result def __str__(self)return 'self __class__ __name__id(self)self __attrnames()my class' name my address name=value list if __name__ ='__main__'import testmixin testmixin tester(listinstanceall the code in this section runs in both python and coding notethis code exhibits classic comprehension patternand you could save some program real estate by implementing the __attrnames method here more concisely with generator expression that is triggered by the string join methodbut it' arguably less clear--expressions that wrap lines like this should generally make you consider simpler coding alternativesdef __attrnames(self)return 'join('\ % =% \ (attrself __dict__ [attr]for attr in sorted(self __dict__)listinstance uses some previously explored tricks to extract the instance' class name and attributeseach instance has built-in __class__ attribute that references the class from which it was createdand each class has __name__ attribute that references the name in the headerso the expression self __class__ __name__ fetches the name of an instance' class multiple inheritance"mix-inclasses