New-style and classic classes

Classes and instances come in two flavors: old-style or classic, and new-style.

Up to Python 2.1, old-style classes were the only flavour available to the user. The concept of (old-style) class is unrelated to the concept of type: if x is an instance of an old-style class, then x.__class__ designates the class of x, but type(x) is always <type 'instance'>. This reflects the fact that all old-style instances, independently of their class, are implemented with a single built-in type (see type-instance).

New-style classes were introduced in Python 2.2 to unify classes and types. A n