Fluent Python, 2nd Edition

Chapter 14. Inheritance: For Better or for Worse

[...] we needed a better theory about inheritance entirely (and still do). For example, inheritance and instancing (which is a kind of inheritance) muddles both pragmatics (such as factoring code to save space) and semantics (used for way too many tasks such as: specialization, generalization, speciation, etc.).

Alan Kay, “The Early History of Smalltalk”¹

This chapter is about inheritance and subclassing. I will assume a basic understanding of these concepts, which you may know from reading The Python Tutorial or from experience with another mainstream object-oriented language, such as Java, C#, or C++. Here we’ll focus on four characteristics of Python:

• The super() function

• The pitfalls of subclassing from built-in types

• Multiple inheritance and method resolution order

• Mixin classes

Multiple inheritance is the ability of a class to have more than one base class. C++ supports it; Java and C# don’t. Many consider multiple inheritance more trouble than it’s worth. It was deliberately left out of Java after its perceived abuse in early C++ codebases.

This chapter introduces multiple inheritance for those who have never used it, and provides some guidance on how to cope with single or multiple inheritance if you must use it.

As of 2021, there is a significant backlash against overuse of inheritance in general—not only multiple inheritance—because superclasses and subclasses are tightly coupled. Tight coupling means that ...