Pro Python Best Practices: Debugging, Testing and Maintenance

383 Pages·2017·4.25 MB·English

by  Kristian Rother

Kristian Rother
Pro Python Best Practices
Debugging, Testing and Maintenance
Kristian Rother
Berlin, Germany
Any source code or other supplementary material referenced by the author in this
book is available to readers on GitHub via the book’s product page, located at
www.apress.com/9781484222409 . For more detailed information,
please visit http://www.apress.com/source-code .
ISBN 978-1-48422240-9 e-ISBN 978-1-4842-2241-6
DOI 10.1007/978-1-4842-2241-6
Library of Congress Control Number: 2017936044
© Kristian Rother 2017
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To my parents
Preface
Writing good Python programs is difficult. Once your programs grow past a few
lines, they are inherently prone to errors of all kind. There are many pitfalls
unknown to the apprentice developer, but not because Python as a language is
difficult to use. To the contrary, the overabundant opportunities Python provides
make it difficult to figure out what matters in your daily practice. Instead of
trying to cover the entire world of Python, this book focuses on a few essential
practices used by most professional Python programmers. These Best Practices
will help you to debug programs, write automated tests for your software, and
keep it in a state that can be maintained with reasonable effort. I have picked
techniques useful for Python developers in data analysis, web development, and
scientific software development alike. If you feel you have mastered the basics
of Python and want to improve the way you write programs, this book is here to
help you raise the bar.
Acknowledgments
First of all, I would like to thank my mentors: Wolfgang Vahrson, who
introduced me to Python; and Christoph Gille, Cornelius Frömmel, and Ulf
Leser, whose guidance helped me to develop my programming skills. I am
thankful for the Python projects I had the pleasure to work on with Kaja
Milanowska, Anna Philipps, Joanna Kasprzak, Tomasz Puton, Justyna
Wojtczak, Pawel Skiba, Marcin Feder, Michal Gajda, Staszek Dunin-Horkawicz,
Michal Boniecki, Wojciech Potrzebowski, Natalia Szostak, Michal Pietal, Silke
Trissl, Christian Tismer, and Raphael Bauer. Without these people, I would not
be in the position to write anything about Python.
I am grateful for many opportunities to teach Python provided by Pedro
Fernandes, Allegra Via, Jasmin Touati, Veit Schiele, Jose Quesada, Janick
Mathys, Martin Hoste, Julia Rose, Eryk Hajecki, and Edward Jenkins. I recall
many fruitful conversations inside and outside of training rooms with most of
these people about learning programming skills.
Credit goes to Dinu Gherman, Sebastian Thieme, Daniel Godoy, and Markus
Rother, who reviewed my early notes for the book and provided plenty of
valuable feedback on the structure. An especially big “Thank You” is reserved
for my Technical Reviewer, Michael Thomas, who undertook the ordeal of
reading through the early drafts of all chapters and provided constructive
reviews that motivated me to improve the material.
This book would not have been possible without the diligence and patience
of my Coordinating Editor, Mark Powers, who displayed a great deal of
professionalism dealing with both the ups and downs of a manuscript and whose
merit it is that the book actually got finished. The support of Development Editor
Matthew Moodie and Acquisitions Editor Stephen Anglin was equally
indispensable during the last 12 months.
Finally, I would like to thank my family for the support that gave me the
courage to finish the book. My wife Magdalena Rother, being a fabulous Python
developer, gave me counsel throughout the writing process, including critically
examining my code, testing Python tools with me, debating programming
practices after midnight, and making every other moment with her a moment
well spent.
Contents
Chapter 1: Introduction
A Lesson in Humility
The Case for Best Practices in Python
The Origin of Best Practices
Hacking
Software Engineering
Agile
Software Craftsmanship
Who This Book Is For
What This Book Is About
Part 1: Debugging
Part 2: Automated Testing
Part 3: Maintenance
Further Benefits
The MazeRun Game
How to Use This Book?
Install Python 3
Install the Pygame Library
Install a Text Editor
Download the Source Code Examples
Part I: Debugging
Chapter 2: Exceptions in Python
Exceptions Are Defects We Know About
Reading the Code
SyntaxError
Best Practices for Debugging SyntaxErrors
Examining the Error Message
The Error Type
The Error Description
The Traceback
Deduction
Catching Exceptions
Best Practices for Debugging IOErrors
Errors and Defects
Where Do Defects Come From?
The Correct Code
Best Practices
Chapter 3: Semantic Errors in Python
Comparing Expected and Factual Output
Defects
Defects in Variable Assignments
Multiple Initialization
Accidental Assignment
Accidental Comparison
Wrong Variables in an Expression
Swapped Literals in Expression
Defects in Indexing
Creating Wrong Indices
Using Wrong Indices
Defects in Control Flow Statements
Defects in Boolean Expressions
Defects with Indentation
Defects in Using Functions
Omitting a Function Call
Missing Return Statement
Not Storing the Return Value
Error Propagation
Best Practices
Chapter 4: Debugging with the Scientific Method
Applying the Scientific Method
Reproducing the Error