Better Python Code

David Mertz has been a member of the Python community for 25 years. He has taught Python to scientists, developers coming from other languages, and to programming neophytes. He was a director of the Python Software Foundation (PSF) for six years and continues to serve on, or chair, a variety of PSF working groups. David is the author of several technical books and has given keynote addresses at numerous international programming conferences.

"You'll not just be aspiring to be an expert anymore after practicing through Better Python Code: A Guide for Aspiring Experts, you'll be one of them! Learn from David Mertz, who's been making experts through his writing and training for the past 20 years."--Iqbal Abdullah, past Chair, PyCon Asia Pacific, and past board member, PyCon Japan"In Better Python Code: A Guide for Aspiring Experts, David Mertz serves up bite-sized chapters of Pythonic wisdom in this must-have addition to any serious Python programmer's collection. This book helps bridge the gap from beginner to advanced Python user, but even the most seasoned Python programmer can up their game with Mertz's insight into the ins and outs of Python."--Katrina Riehl, President, NumFOCUS"What separates ordinary coders from Python experts? It's more than just knowing best practices--it's understanding the benefits and pitfalls of the many aspects of Python, and knowing when and why to choose one approach over another. In this book David draws on his more than 20 years of involvement in the Python ecosystem and his experience as a Python author to make sure that the readers understand both what to do and why in a wide variety of scenarios."--Naomi Ceder, past Chair, Python Software Foundation"Like a Pythonic BBC, David Mertz has been informing, entertaining, and educating the Python world for over a quarter of a century, and he continues to do so here in his own pleasantly readable style."--Steve Holden, past Chair, Python Software Foundation"Being expert means someone with a lot of experience. David's latest book provides some important but common problems that folks generally learn only after spending years of doing and fixing. I think this book will provide a much quicker way to gather those important bits and help many folks across the world to become better."--Kushal Das, CPython Core Developer and Director, Python Software Foundation"This book is for everyone: from beginners, who want to avoid hard-to-find bugs, all the way to experts looking to write more efficient code. David Mertz has compiled a great set of useful idioms that will make your life as a programmer easier and your users happier."--Marc-André Lemburg, past Chair, EuroPython, and past Director, Python Software Foundation

• Foreword xviiPreface xixAcknowledgments xxvAbout the Author xxviiIntroduction 1Chapter 1: Looping Over the Wrong Things 31.1 (Rarely) Generate a List for Iteration 31.2 Use enumerate() Instead of Looping Over an Index 61.3 Don't Iterate Over dict.keys() When You Want dict.items() 81.4 Mutating an Object During Iteration 91.5 for Loops Are More Idiomatic Than while Loops 121.6 The Walrus Operator for "Loop-and-a-Half" Blocks 131.7 zip() Simplifies Using Multiple Iterables 151.8 zip(strict=True) and itertools.zip_longest() 171.9 Wrapping Up 20Chapter 2: Confusing Equality with Identity 212.1 Late Binding of Closures 212.2 Overchecking for Boolean Values 252.3 Comparing x == None 282.4 Misunderstanding Mutable Default Arguments 292.5 Copies versus References to Mutable Objects 332.6 Confusing is with == (in the Presence of Interning) 352.7 Wrapping Up 37Chapter 3: A Grab Bag of Python Gotchas 393.1 Naming Things 393.2 Quadratic Behavior of Naive String Concatenation 523.3 Use a Context Manager to Open a File 563.4 Optional Argument key to .sort() and sorted() 593.5 Use dict.get() for Uncertain Keys 623.6 Wrapping Up 64Chapter 4: Advanced Python Usage 674.1 Comparing type(x) == type(y) 674.2 Naming Things (Revisited) 714.3 Keep Less-Used Features in Mind 794.4 Type Annotations Are Not Runtime Types 984.5 Wrapping Up 105Chapter 5: Just Because You Can, It Doesn't Mean You Should... 1075.1 Metaclasses 1075.2 Monkeypatching 1125.3 Getters and Setters 1155.4 It's Easier to Ask for Forgiveness Than Permission 1185.5 Structural Pattern Matching 1215.6 Regular Expressions and Catastrophic Backtracking 1235.7 Wrapping Up 126Chapter 6: Picking the Right Data Structure 1296.1 collections.defaultdict 1296.2 collections.Counter 1326.3 collections.deque 1356.4 collections.ChainMap 1386.5 Dataclasses and Namedtuples 1416.6 Efficient Concrete Sequences 1466.7 Wrapping Up 150Chapter 7: Misusing Data Structures 1537.1 Quadratic Behavior of Repeated List Search 1537.2 Deleting or Adding Elements to the Middle of a List 1577.3 Strings Are Iterables of Strings 1637.4 (Often) Use enum Rather Than CONSTANT 1667.5 Learn Less Common Dictionary Methods 1697.6 JSON Does Not Round-Trip Cleanly to Python 1747.7 Rolling Your Own Data Structures 1787.8 Wrapping Up 187Chapter 8: Security 1898.1 Kinds of Randomness 1908.2 Putting Passwords or Other Secrets in "Secure" Source Code 1958.3 "Rolling Your Own" Security Mechanisms 1988.4 Use SSL/TLS for Microservices 2018.5 Using the Third-Party requests Library 2058.6 SQL Injection Attacks When Not Using DB-API 2088.7 Don’t Use assert to Check Safety Assumptions 2128.8 Wrapping Up 215Chapter 9: Numeric Computation in Python 2179.1 Understanding IEEE-754 Floating Point Numbers 2179.2 Numeric Datatypes 2289.3 Wrapping Up 239Appendix: Topics for Other Books 241A.1 Test-Driven Development 241A.2 Concurrency 242A.3 Packaging 243A.4 Type Checking 243A.5 Numeric and Dataframe Libraries 244Index 245