Book Image

Modular Programming with Python

By : Erik Westra
Book Image

Modular Programming with Python

By: Erik Westra

Overview of this book

Python has evolved over the years and has become the primary choice of developers in various fields. The purpose of this book is to help readers develop readable, reliable, and maintainable programs in Python. Starting with an introduction to the concept of modules and packages, this book shows how you can use these building blocks to organize a complex program into logical parts and make sure those parts are working correctly together. Using clearly written, real-world examples, this book demonstrates how you can use modular techniques to build better programs. A number of common modular programming patterns are covered, including divide-and-conquer, abstraction, encapsulation, wrappers and extensibility. You will also learn how to test your modules and packages, how to prepare your code for sharing with other people, and how to publish your modules and packages on GitHub and the Python Package Index so that other people can use them. Finally, you will learn how to use modular design techniques to be a more effective programmer.
Table of Contents (16 chapters)
Modular Programming with Python
About the Author
About the Reviewer

Introducing Python packages

In the same way that Python modules allow you to organize your functions and classes into separate Python source files, Python packages allow you to group multiple modules together.

A Python package is a directory with certain characteristics. For example, consider the following directory of Python source files:

This Python package, called animals, contains five Python modules: cat, cow, dog, horse, and sheep. There is also a special file with the rather unusual name This file is called a package initialization file; the presence of this file tells the Python system that this directory contains a package. The package initialization file can also be used to initialize the package (hence the name) and can also be used to make importing the package easier.


Starting with Python version 3.3, packages don't always need to include an initialization file. However, packages without an initialization file (called namespace packages) are still quite uncommon and are only used in very specific circumstances. To keep things simple, we will be using regular packages (with the file) throughout this book.

Just like we used the module name when calling a function within a module, we use the package name when referring to a module within a package. For example, consider the following code:

import animals.cow

In this example, the speak() function is defined within the module, which itself is part of the animals package.

Packages are a great way of organizing more complicated Python programs. You can use them to group related modules together, and you can even define packages inside packages (called nested packages) to keep your program super-organized.

Note that the import statement (and the related from...import statement) can be used in a variety of ways to load packages and modules into your program. We have only scratched the surface here, showing you what modules and packages look like in Python so that you can recognize them when you see them in a program. We will be looking at the way modules and packages can be defined and imported in much more depth in Chapter 3, Using Modules and Packages.


Downloading the example code

The code bundle for the book is also hosted on GitHub at We also have other code bundles from our rich catalog of books and videos available at Check them out!