Expert Python Programming - Third Edition

Template

Template helps design a generic algorithm by defining abstract steps, which are implemented in subclasses. This pattern uses the Liskov Substitution Principle (LSP), which is defined by Wikipedia as follows:

"If S is a subtype of T, then objects of type T in a program may be replaced with objects of type S without altering any of the desirable properties of that program."

In other words, an abstract class can define how an algorithm works through steps that are implemented in concrete classes. The abstract class can also give a basic or partial implementation of the algorithm, and let developers override its parts. For instance, some methods of the Queue class in the queue module can be overridden to make its behavior vary.

Let's ...