Fluent Python

Chapter 6. Design Patterns with First-Class Functions

Conformity to patterns is not a measure of goodness.¹

Ralph Johnson, Coauthor of the Design Patterns classic

Although design patterns are language-independent, that does not mean every pattern applies to every language. In his 1996 presentation, “Design Patterns in Dynamic Languages”, Peter Norvig states that 16 out of the 23 patterns in the original Design Patterns book by Gamma et al. become either “invisible or simpler” in a dynamic language (slide 9). He was talking about Lisp and Dylan, but many of the relevant dynamic features are also present in Python.

The authors of Design Patterns acknowledge in their Introduction that the implementation language determines which patterns are relevant:

The choice of programming language is important because it influences one’s point of view. Our patterns assume Smalltalk/C++-level language features, and that choice determines what can and cannot be implemented easily. If we assumed procedural languages, we might have included design patterns called “Inheritance,” “Encapsulation,” and “Polymorphism.” Similarly, some of our patterns are supported directly by the less common object-oriented languages. CLOS has multi-methods, for example, which lessen the need for a pattern such as Visitor.²

In particular, in the context of languages with first-class functions, Norvig suggests rethinking the Strategy, Command, Template Method, and Visitor patterns. The general idea is: you can replace ...