Python's super() is one of those aspects of the language that many developers use without really understanding what it does or how it works. To many people, super() is simply how you access your base-class's implementation of a method. And while this is true, it's far from the full story.

In this series I want to look at the mechanics and some of the theory behind super() . I want to show that, far from just letting you access your base-class, Python's super() is the key to some interesting and elegant design options that promote composability, separation of concerns, and long-term maintainability. In this first article I'll introduce a small set of classes, and in these classes we'll find a bit of a mystery. In subsequent articles we'll investigate this mystery by seeing how Python's super() really works, looking at topics like method resolution order, the C3 algorithm, and proxy objects.

In the end, you'll find that super() is both more complex than you probably expected, yet also surprisingly elegant and easy-to-understand. This improved understanding of super() will help you understand and appreciate Python on at a deeper level, and it will give you new tools for developing your own Python code.

A note on Python versions

This series is written using Python 3, and some of the examples and concepts don't apply completely to Python 2. In particular, this series assumes that classes are "new-style" classes. ((For a discussion of the difference between "old-style" and "new-style" classes, see the Python wiki.)) In Python 3 all classes are new-style, while in Python 2 you have to explicitly inherit from object to be a new-style class.

For example, where we might use the following Python 3 code in this series:

class IntList : . . .

the equivalent Python 2 code would be:

class IntList ( object ): . . .

Also, throughout this series we'll call super() with no arguments. This is only supported in Python 3, but it has an equivalent form in Python 2. In general, when you see a method like this:

class IntList : def add ( self , x ): super () . add ( x )

the equivalent Python 2 code has to pass the class name and self to super() , like this:

class IntList : def add ( self , x ): super ( IntList , self ) . add ( x )

If any other Python2/3 differences occur in the series, I'll be sure to point them out.