Two nitpicky comments. > Even if, right now, we were to change it to _note2, the maintainer of A could, in any future release of A, add a new _note2 variable w

Two nitpicky comments. > Even if, right now, we were to change it to _note2, the maintainer of A could, in any future release of A, add a new _note2 variable which conflicts with something B is using. This is why Python offers actual namespacing of properties and methods in the form of a double underscore (__). Double underscore prepends an underscore and the class name to the private property name which prevents these sorts of collisions. class Bprime(object): def __init__(self, a): for var in dir(a): setattr(self, var, getattr(a, var)) > Uh oh. Looks like composition is worse than inheritance. This is not composition.