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Pro Python 3: Features and Tools for Professional Development

Pro Python 3: Features and Tools for Professional Development

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Third Edition

by J. Burton Browning Marty Alchin


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Book Details
 Price
 4.00
 Pages
 468 p
 File Size 
 6,088 KB
 File Type
 PDF format
 ISBN-13
 978-1-4842-4384-8 (pbk)
 978-1-4842-4385-5 (electronic)  
 Copyright©   
 2019 by J. Burton Browning
 and Marty Alchin 

About the Authors
Dr. J. Burton Browning earned his doctorate from North Carolina State University.
He has conducted research in areas including distance learning, programming, and
instructional technology. As a lifelong learner and someone who has interests in topics
such as programming, photography, robotics, car restoration, woodworking, hunting,
reading, fishing, and archery, he is never at a loss for something to do. The
art and joy of serving as a professor suits his inquisitive nature. Dr. Browning’s
previous publications include works on Cross-Functional Learning Teams (CFLT), the
Utopian School (teacher-led school model), computer programming (several languages),
open-source software, healthcare statistics and data mining, CNC plasma cutter operation,
educational technology, biography, mobile learning, online teaching, and more.

By day, Marty Alchin works as a senior software engineer at Heroku, and
after that, he writes and codes for fun and community. His blog can be found at
http://martyalchin.com and he has profiles on many other services under the name
Gulopine. In particular, his code can be found on GitHub and his random thoughts
are on Twitter. He also accepts tips for his open source work at https://gittip.com/gulopine.

About the Technical Reviewer
Michael Thomas has worked in software development
for over 20 years as an individual contributor, team lead,
program manager, and vice president of engineering.
Michael has over 10 years of experience working with mobile
devices. His current focus is in the medical sector, using
mobile devices to accelerate information transfer between
patients and healthcare providers.

Introduction
This third edition expands on Marty's original work. Found in each chapter of this third
edition are useful libraries that any Python programmer will find of value. Use what you
learn for your own projects and enjoyment!
J. Burton Browning
When I wrote my first book, Pro Django, I didn’t have much of an idea what my readers
would find interesting. I had gained a lot of information I thought would be useful for
others to learn, but I didn’t really know what would be the most valuable thing they’d
take away. As it turned out, in nearly 300 pages, the most popular chapter in the book
barely mentioned Django at all. It was about Python.
The response was overwhelming. There was clearly a desire to learn more about
how to go from a simple Python application to a detailed framework like Django. It’s all
Python code, but it can be hard to understand based on even a reasonably thorough
understanding of the language. The tools and techniques involved require some extra
knowledge that you might not run into in general use.
This gave me a new goal with Pro Python: to take you from proficient to professional.
Being a true professional requires more experience than you can get from a book, but I
want to at least give you the tools you’ll need. Combined with the rich philosophy of the
Python community, you’ll find plenty of information to take your code to the next level.
Marty Alchin

Table of Contents
About the Authors  xv
About the Technical Reviewer  xvii
Acknowledgments  xix
Introduction  xxi
Chapter 1: Principles and Philosophy  1
The Zen of Python ......................................................................................................................... 2
Beautiful Is Better Than Ugly ................................................................................................... 3
Explicit Is Better Than Implicit ................................................................................................. 4
Simple Is Better Than Complex ............................................................................................... 5
Complex Is Better Than Complicated ....................................................................................... 6
Flat Is Better Than Nested ....................................................................................................... 6
Sparse Is Better Than Dense ................................................................................................... 8
Readability Counts ................................................................................................................... 9
Special Cases Aren’t Special Enough to Break the Rules ...................................................... 10
Practicality Beats Purity ........................................................................................................ 10
Errors Should Never Pass Silently ......................................................................................... 11
Unless Explicitly Silenced ...................................................................................................... 14
In the Face of Ambiguity, Refuse the Temptation to Guess .................................................... 15
There Should Be One—and Preferably Only One—Obvious Way to Do It ............................. 15
Although That Way May Not Be Obvious at First, Unless You’re Dutch .................................. 17
Now Is Better Than Never ...................................................................................................... 17
Although Never Is Often Better Than Right Now .................................................................... 18
If the Implementation Is Hard to Explain, It’s a Bad Idea ....................................................... 18
If the Implementation Is Easy to Explain, It May Be a Good Idea .......................................... 19
Namespaces Are One Honking Great Idea: Let’s Do More of Those! ..................................... 19
Don’t Repeat Yourself .................................................................................................................. 20
Loose Coupling ............................................................................................................................ 21
The Samurai Principle ................................................................................................................. 22
The Pareto Principle .................................................................................................................... 22
The Robustness Principle ........................................................................................................... 23
Backward Compatibility .............................................................................................................. 25
Taking It With You ........................................................................................................................ 26
Chapter 2: Advanced Basics  27
General Concepts ........................................................................................................................ 27
Iteration ................................................................................................................................. 27
Caching .................................................................................................................................. 29
Transparency ......................................................................................................................... 30
Control Flow ................................................................................................................................ 32
Catching Exceptions .............................................................................................................. 32
Exception Chains ................................................................................................................... 37
When Everything Goes Right ................................................................................................. 39
Proceeding Regardless of Exceptions ................................................................................... 41
Optimizing Loops ................................................................................................................... 43
The with Statement ............................................................................................................... 44
Conditional Expressions ........................................................................................................ 46
Iteration ....................................................................................................................................... 49
Sequence Unpacking ............................................................................................................. 50
List Comprehensions ............................................................................................................. 52
Generator Expressions ........................................................................................................... 53
Set Comprehensions ............................................................................................................. 55
Dictionary Comprehensions .................................................................................................. 56
Chaining Iterables Together ................................................................................................... 56
Zipping Iterables Together ..................................................................................................... 57
Collections .................................................................................................................................. 58
Sets ....................................................................................................................................... 58
Named Tuples ........................................................................................................................ 65
Ordered Dictionaries .............................................................................................................. 66
Dictionaries with Defaults ..................................................................................................... 67
Importing Code ............................................................................................................................ 68
Fallback Imports .................................................................................................................... 68
Importing from the Future ..................................................................................................... 70
Using __all__ to Customize Imports ..................................................................................... 71
Relative Imports .................................................................................................................... 74
The __import__( ) Function ................................................................................................... 74
The importlib Module ............................................................................................................ 78
Exciting Python Extensions: Random Number Beacon at NIST ................................................... 79
How to Install the NIST Beacon Library ................................................................................. 80
Simple Example to Get a Value .............................................................................................. 80
Example to Simulate Rolling Coin Flipping a Certain # Times and Display Heads or Tails .... 81
Taking It With You ........................................................................................................................ 81
Chapter 3: Functions 83
Arguments .................................................................................................................................. 84
Planning for Flexibility ........................................................................................................... 84
Variable Positional Arguments ............................................................................................... 85
Variable Keyword Arguments ................................................................................................ 87
Combining Different Kinds of Arguments .............................................................................. 89
Invoking Functions with Variable Arguments ........................................................................ 92
Passing Arguments ................................................................................................................ 93
Introspection .......................................................................................................................... 95
Example: Identifying Argument Values .................................................................................. 96
Example: A More Concise Version ........................................................................................ 100
Example: Validating Arguments ........................................................................................... 102
Decorators ................................................................................................................................ 105
Closures ............................................................................................................................... 107
Wrappers ............................................................................................................................. 109
Decorators with Arguments ................................................................................................. 111
Decorators with—or without—Arguments ......................................................................... 114
Example: Memoization ........................................................................................................ 116
Example: A Decorator to Create Decorators ........................................................................ 118
Function Annotations ................................................................................................................ 120
Example: Type Safety ........................................................................................................... 121
Factoring Out the Boilerplate ............................................................................................... 131
Example: Type Coercion ....................................................................................................... 134
Annotating with Decorators ................................................................................................. 137
Example: Type Safety as a Decorator .................................................................................. 137
Generators ................................................................................................................................ 143
Lambdas ................................................................................................................................... 146
Introspection ............................................................................................................................. 148
Identifying Object Types ...................................................................................................... 149
Modules and Packages ....................................................................................................... 150
Docstrings ........................................................................................................................... 151
Exciting Python Extensions: Statistics ...................................................................................... 154
Install Pandas and Matplotlib .............................................................................................. 154
Make a Text File of Data ...................................................................................................... 155
Use Pandas to Display Data ................................................................................................. 155
Running Some Data Analysis ............................................................................................... 156
Plotting with Matplotlib ....................................................................................................... 157
Types of Charts .................................................................................................................... 158
Combine Matplotlib with Pandas ......................................................................................... 158
Taking It with You ...................................................................................................................... 159
Chapter 4: Classes  161
Inheritance ................................................................................................................................ 161
Multiple Inheritance ............................................................................................................. 165
Method Resolution Order ..................................................................................................... 166
Example: C3 Algorithm ........................................................................................................ 171
Using super( ) to Pass Control to Other Classes ................................................................... 179
Introspection ........................................................................................................................ 184
How Classes Are Created .......................................................................................................... 186
Creating Classes at Runtime ............................................................................................... 188
Metaclasses ........................................................................................................................ 190
Example: Plugin Framework ................................................................................................ 192
Controlling the Namespace ................................................................................................. 196
Attributes .................................................................................................................................. 198
Properties ............................................................................................................................ 198
Descriptors .......................................................................................................................... 201
Methods .................................................................................................................................... 204
Unbound Methods ............................................................................................................... 204
Bound Methods ................................................................................................................... 205
Class Methods ..................................................................................................................... 207
Static Methods .................................................................................................................... 209
Assigning Functions to Classes and Instances .................................................................... 210
Magic Methods ......................................................................................................................... 211
Creating Instances ............................................................................................................... 211
Example: Automatic Subclasses .......................................................................................... 213
Dealing with Attributes ........................................................................................................ 215
String Representations ........................................................................................................ 218
Exciting Python Extensions: Iterators ........................................................................................ 221
Taking It With You ...................................................................................................................... 223
Chapter 5: Common Protocols  225
Basic Operations ....................................................................................................................... 226
Mathematical Operations .................................................................................................... 228
Bitwise Operations .............................................................................................................. 234
Variations ............................................................................................................................. 236
Numbers ................................................................................................................................... 240
Sign Operations ................................................................................................................... 242
Comparison Operations ....................................................................................................... 243
Iterables .................................................................................................................................... 244
Example: Repeatable Generators ........................................................................................ 248
Sequences ................................................................................................................................ 250
Mappings .................................................................................................................................. 257
Callables ................................................................................................................................... 259
Context Managers ..................................................................................................................... 260
Exciting Python Extensions: Scrapy .......................................................................................... 262
Installation ........................................................................................................................... 263
Running Scrapy ................................................................................................................... 263
Project Setup ....................................................................................................................... 263
Retrieve Web Data with Scrapy ........................................................................................... 265
View a Web Page via Scrapy ............................................................................................... 265
Shell Options ....................................................................................................................... 265
Taking It With You ...................................................................................................................... 267
Chapter 6: Object Management  269
Namespace Dictionary .............................................................................................................. 270
Example: Borg Pattern ......................................................................................................... 270
Example: Self-Caching Properties ....................................................................................... 275
Garbage Collection .................................................................................................................... 280
Reference Counting ............................................................................................................. 281
Cyclical References ............................................................................................................. 283
Weak References ................................................................................................................. 287
Pickling ..................................................................................................................................... 289
Copying ..................................................................................................................................... 296
Shallow Copies .................................................................................................................... 297
Deep Copies ......................................................................................................................... 299
Exciting Python Extensions: Beautiful Soup .............................................................................. 301
Installing Beautiful Soup ..................................................................................................... 302
Using Beautiful Soup ........................................................................................................... 302
Taking It With You ...................................................................................................................... 303
Chapter 7: Strings  305
Bytes ......................................................................................................................................... 305
Simple Conversion: chr( ) and ord( ) ..................................................................................... 306
Complex Conversion: The Struct Module ............................................................................. 307
Text ........................................................................................................................................... 312
Unicode ................................................................................................................................ 312
Encodings ............................................................................................................................ 313
Simple Substitution ................................................................................................................... 316
Formatting ................................................................................................................................ 319
Looking Up Values Within Objects ....................................................................................... 321
Distinguishing Types of Strings ........................................................................................... 321
Standard Format Specification ............................................................................................ 322
Example: Plain Text Table of Contents ................................................................................. 324
Custom Format Specification .............................................................................................. 326
Exciting Python Extensions: Feedparser ................................................................................... 327
Feedparser .......................................................................................................................... 327
How to Install ....................................................................................................................... 328
How to Use .......................................................................................................................... 328
Taking It With You ...................................................................................................................... 329
Chapter 8: Documentation  331
Proper Naming .......................................................................................................................... 332
Comments ................................................................................................................................. 333
Docstrings ................................................................................................................................. 334
Describe What the Function Does ....................................................................................... 335
Explain the Arguments ........................................................................................................ 335
Don’t Forget the Return Value ............................................................................................. 336
Include Any Expected Exceptions ........................................................................................ 336
Documentation Outside the Code ............................................................................................. 336
Installation and Configuration ............................................................................................. 337
Tutorials ............................................................................................................................... 337
Reference Documents ......................................................................................................... 337
Documentation Utilities ............................................................................................................. 338
Formatting ........................................................................................................................... 339
Links .................................................................................................................................... 340
Sphinx .................................................................................................................................. 343
Exciting Python Extensions: NumPy .......................................................................................... 343
Install NumPy ...................................................................................................................... 344
Using NumPy ....................................................................................................................... 344
Working With NumPy Arrays ................................................................................................ 346
Statistical Measures ............................................................................................................ 347
Taking It With You ...................................................................................................................... 347
Chapter 9: Testing 349
Test-Driven Development .......................................................................................................... 349
Doctests .................................................................................................................................... 350
Formatting Code .................................................................................................................. 350
Representing Output ............................................................................................................ 351
Integrating With Documentation .......................................................................................... 353
Running Tests ...................................................................................................................... 354
The unittest Module .................................................................................................................. 356
Setting Up ............................................................................................................................ 356
Writing Tests ........................................................................................................................ 357
Other Comparisons .............................................................................................................. 363
Testing Strings and Other Sequence Content ...................................................................... 363
Testing Exceptions ............................................................................................................... 364
Testing Identity .................................................................................................................... 366
Tearing Down ....................................................................................................................... 367
Providing a Custom Test Class .................................................................................................. 368
Changing Test Behavior ....................................................................................................... 368
Exciting Python Extensions: Pillow ............................................................................................ 369
How to Install Pillow (PIL) .................................................................................................... 369
Image Display: Determine File Size, Type, and Display It ..................................................... 369
Image Processing: Crop a Portion of an Image .................................................................... 370
Image Processing: Changing Image Orientation .................................................................. 370
Image Processing: Filters .................................................................................................... 371
Taking It With You ...................................................................................................................... 371
Chapter 10: Distribution 373
Licensing ................................................................................................................................... 373
GNU General Public License ................................................................................................ 373
Affero General Public License ............................................................................................. 375
GNU Lesser General Public License ..................................................................................... 376
Berkeley Software Distribution License .............................................................................. 376
Other Licenses ..................................................................................................................... 378
Packaging ................................................................................................................................. 378
setup.py ............................................................................................................................... 379
MANIFEST.in ........................................................................................................................ 382
The sdist Command ............................................................................................................. 384
Distribution ............................................................................................................................... 386
Exciting Python Extensions: Secrets Module ............................................................................ 387
Random Numbers ................................................................................................................ 388
Password Generation .......................................................................................................... 388
Taking It With You ...................................................................................................................... 390
Chapter 11: Sheets: A CSV Framework 391
Building a Declarative Framework ............................................................................................ 392
Introducing Declarative Programming ................................................................................. 393
To Build or Not to Build? ...................................................................................................... 394
Building the Framework ............................................................................................................ 396
Managing Options ............................................................................................................... 397
Defining Fields ..................................................................................................................... 401
Attaching a Field to a Class ................................................................................................. 403
Adding a Metaclass ............................................................................................................. 405
Bringing It Together ............................................................................................................. 409
Ordering Fields .......................................................................................................................... 410
DeclarativeMeta.__prepare__( ) .......................................................................................... 411
Column.__init__( ) ............................................................................................................... 414
Column.__new__( ) ............................................................................................................. 418
CounterMeta.__call__( ) ...................................................................................................... 419
Choosing an Option ............................................................................................................. 421
Building a Field Library ............................................................................................................. 421
StringField ........................................................................................................................... 423
IntegerColumn ..................................................................................................................... 424
FloatColumn ........................................................................................................................ 424
DecimalColumn ................................................................................................................... 425
DateColumn ......................................................................................................................... 426
Getting Back to CSV .................................................................................................................. 431
Checking Arguments ........................................................................................................... 433
Populating Values ................................................................................................................ 436
The Reader .......................................................................................................................... 439
The Writer ............................................................................................................................ 444
Taking It With You ...................................................................................................................... 448
Index   449


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Who This Book Is For
The goal is to bring intermediate programmers to a more advanced level; we wrote
this book with the expectation that you’ll already be familiar with Python on some
basic level. You should be comfortable using the interactive interpreter, writing control
structures, and [using] a basic object-oriented approach.
That’s not a very difficult prerequisite. If you’ve tried your hand at writing a Python
application—even if you haven’t released it into the wild, or even finished it—you likely
have all the necessary knowledge to get started. The rest of the information you’ll need is
contained in these pages.

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