Table Of Content[ 1 ]
Modular Programming with
Python
Introducing modular techniques for building
sophisticated programs using Python
Erik Westra
BIRMINGHAM - MUMBAI
Modular Programming with Python
Copyright © 2016 Packt Publishing
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First published: May 2016
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ISBN 978-1-78588-448-1
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Credits
Author Project Coordinator
Erik Westra Nikhil Nair
Reviewer Proofreader
Mike Driscoll Safis Editing
Commissioning Editor Indexer
Priya Singh Hemangini Bari
Acquisition Editor Graphics
Dharmesh Parmar Disha Haria
Content Development Editor Production Coordinator
Arun Nadar Arvindkumar Gupta
Technical Editor Cover Work
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Copy Editor
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About the Author
Erik Westra has been a professional software developer for over 25 years, and
has worked almost exclusively in Python for the past decade. Erik's early interest in
graphical user interface design led to the development of one of the most advanced
urgent courier dispatch systems used by messenger and courier companies
worldwide. In recent years, Erik has been involved in the design and implementation
of systems matching seekers and providers of goods and services across a range of
geographical areas, as well as real-time messaging and payments systems. This work
has included the creation of real-time geocoders and map-based views of constantly
changing data. Erik is based in New Zealand, and works for companies worldwide.
Erik is also the author of the Packt titles Python Geospatial Development, Python
Geospatial Analysis, and Building Mapping Applications with QGIS.
I would like to thank Ruth for being so awesome, and my
children for their patience. Without you, none of this would
have been possible.
About the Reviewer
Mike Driscoll has been programming in Python since 2006. He enjoys writing
about Python on his blog at http://www.blog.pythonlibrary.org/. He
co-authored the Core Python Refcard for DZone. Mike has also been a technical
reviewer for Python 3 Object Oriented Programming, Python 2.6 Graphics Cookbook,
Tkinter GUI Application Development Hotshot, and several others. He recently wrote
the book Python 101, and is working on his next book.
I would like to thank my beautiful wife, Evangeline, for always
supporting me. I would also like to thank friends and family for all
that they do to help me. And I would like to thank Jesus Christ for
saving me.
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Table of Contents
Preface v
Chapter 1: Introducing Modular Programming 1
Introducing Python modules 2
Introducing Python packages 4
Using modules and packages to organize a program 6
Why use modular programming techniques? 8
Programming as a process 10
The Python Standard Library 14
Creating your first module 15
Caching 15
Writing a cache module 17
Using the cache 20
Summary 22
Chapter 2: Writing Your First Modular Program 23
The inventory control system 24
Designing the inventory control system 25
The data storage module 26
The user interface module 30
The report generator module 32
The main program 33
Implementing the inventory control system 34
Implementing the data storage module 34
Implementing the user interface module 37
Implementing the report generator module 40
Implementing the main program 42
Summary 46
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Table of Contents
Chapter 3: Using Modules and Packages 47
Modules and packages 47
Packages within packages 49
Initializing a module 50
Initialization functions 51
Initializing a package 52
How to import anything 54
What does the import statement actually do? 54
Using the import statement 56
Relative imports 58
Controlling what gets imported 61
Circular dependencies 63
Running modules from the command line 64
Summary 66
Chapter 4: Using Modules for Real-World Programming 69
Introducing Charter 70
Designing Charter 70
Implementing Charter 74
Implementing the chart.py module 76
Implementing the generator.py module 77
The Pillow library 77
Renderers 78
Testing the code 81
Rendering the title 81
Rendering the x axis 82
The remaining renderers 84
Testing Charter 87
The fly in the ointment – changing requirements 87
Redesigning Charter 89
Refactoring the code 91
Implementing the PDF renderer modules 94
Testing the code 99
Lessons learned 100
Summary 101
Chapter 5: Working with Module Patterns 103
Divide and conquer 103
Abstraction 104
Encapsulation 107
Wrappers 114
Extensible modules 124
Dynamic imports 124
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Table of Contents
Plugins 126
Hooks 127
Summary 129
Chapter 6: Creating Reusable Modules 131
Using modules and packages to share your code 131
What makes a module reusable? 134
Functioning as a standalone unit 134
Using relative imports 136
Noting external dependencies 137
What makes a good reusable module? 137
Solving a general problem 138
Following standard conventions 139
Having clear documentation 140
Examples of reusable modules 143
requests 143
python-dateutil 144
lxml 145
Designing a reusable package 146
Implementing a reusable package 149
Testing our reusable package 158
Summary 160
Chapter 7: Advanced Module Techniques 161
Optional imports 161
Local imports 163
Tweaking imports using sys.path 164
Import gotchas 167
Using an existing name for your module or package 167
Naming a Python script after a module or package 169
Adding package directories to sys.path 170
Executing and importing the same module 172
Using modules and packages with the Python interactive interpreter 173
Dealing with global variables 177
Package configuration 179
Package data 181
Summary 182
Chapter 8: Testing and Deploying Modules 183
Testing modules and packages 183
Testing with the unittest Standard Library module 185
Designing your unit tests 187
Code coverage 187
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