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

Circular dependencies

One of the annoying problems that you are likely to face while working with modules is what is known as circular dependencies. To understand what these are, consider the following two modules:


from module_2 import calc_markup

def calc_total(items):
    total = 0
    for item in items:
        total = total + item['price']
    total = total + calc_markup(total)
    return total


from module_1 import calc_total

def calc_markup(total):
    return total * 0.1

def make_sale(items):
    total_price = calc_total(items)

While this is a contrived example, you can see that module_1 imports something from module_2, and module_2 imports something from module_1. If you tried to run a program containing these two modules, you would see the following error when module_1 is imported:

ImportError: cannot import name calc_total

If you tried to import module_2 instead, you would get a similar error. With the code organized in this way, you're stuck...