Robust Python

Chapter 15. Extensibility

This chapter focuses on extensibility. Extensibility underpins this part of the book; it’s important to understand this key concept. Once you know how extensibility affects robustness, you’ll start seeing opportunities to apply it throughout your codebase. Extensible systems allow other developers to enhance your codebase with confidence, reducing the chance of errors. Let’s examine how.

What Is Extensibility?

Extensibility is the property of systems that allows new functionality to be added without modifying existing parts of your system. Software is not static; it will change. Throughout your codebase’s lifetime, developers will change your software. The soft part of software indicates as much. These changes can be quite large. Think about the times you need to swap out a key piece of your architecture as you scale, or add in new workflows. These changes touch multiple parts of your codebase; simple typechecking won’t catch all errors at this level. After all, you may be redesigning your types completely. The goal of extensible software is to be designed in such a way that you have provided easy extension points for future developers, especially in areas of code that are changed often.

To illustrate this idea, let’s consider a restaurant chain that wants to implement some sort of notification system to help suppliers respond to demand. A restaurant may have a special, or be out of a certain ingredient, or indicate that some ingredient has ...