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About This Fifth Edition

The prior fourth edition of this book published in 2009 covered Python versions 2.6

and 3.0.1 It addressed the many and sometimes incompatible changes introduced in

the Python 3.X line in general. It also introduced a new OOP tutorial, and new chapters

on advanced topics such as Unicode text, decorators, and metaclasses, derived from

both the live classes I teach and evolution in Python “best practice.”

This fifth edition completed in 2013 is a revision of the prior, updated to cover both

Python 3.3 and 2.7, the current latest releases in the 3.X and 2.X lines. It incorporates

1. And 2007’s short-lived third edition covered Python 2.5, and its simpler—and shorter—single-line Python

world. See http://www.rmi.net/~lutz for more on this book’s history. Over the years, this book has grown

in size and complexity in direct proportion to Python’s own growth. Per Appendix C, Python 3.0 alone

introduced 27 additions and 57 changes in the language that found their way into this book, and Python

3.3 continues this trend. Today’s Python programmer faces two incompatible lines, three major

paradigms, a plethora of advanced tools, and a blizzard of feature redundancy—most of which do not

divide neatly between the 2.X and 3.X lines. That’s not as daunting as it may sound (many tools are

variations on a theme), but all are fair game in an inclusive, comprehensive Python text.

xxxiv | Preface

www.it-ebooks.info

all language changes introduced in each line since the prior edition was published, and

has been polished throughout to update and sharpen its presentation. Specifically:

• Python 2.X coverage here has been updated to include features such as dictionary

and set comprehensions that were formerly for 3.X only, but have been back-ported

for use in 2.7.

• Python 3.X coverage has been augmented for new yield and raise syntax; the

__pycache__ bytecode model; 3.3 namespace packages; PyDoc’s all-browser

mode; Unicode literal and storage changes; and the new Windows launcher

shipped with 3.3.

• Assorted new or expanded coverage for JSON, timeit, PyPy, os.popen, generators,

recursion, weak references, __mro__, __iter__, super, __slots__, metaclasses, descriptors, random, Sphinx, and more has been added, along with a general increase

in 2.X compatibility in both examples and narrative.

This edition also adds a new conclusion as Chapter 41 (on Python’s evolution), two

new appendixes (on recent Python changes and the new Windows launcher), and one

new chapter (on benchmarking: an expanded version of the former code timing example). See Appendix C for a concise summary of Python changes between the prior edition

and this one, as well as links to their coverage in the book. This appendix also summarizes initial differences between 2.X and 3.X in general that were first addressed in

the prior edition, though some, such as new-style classes, span versions and simply

become mandated in 3.X (more on what the X’s mean in a moment).

Per the last bullet in the preceding list, this edition has also experienced some growth

because it gives fuller coverage to more advanced language features—which many of us

have tried very hard to ignore as optional for the last decade, but which have now grown

more common in Python code. As we’ll see, these tools make Python more powerful,

but also raise the bar for newcomers, and may shift Python’s scope and definition.

Because you might encounter any of these, this book covers them head-on, instead of

pretending they do not exist.

Despite the updates, this edition retains most of the structure and content of the prior

edition, and is still designed to be a comprehensive learning resource for both the 2.X

and 3.X Python lines. While it is primarily focused on users of Python 3.3 and 2.7—

the latest in the 3.X line and the likely last in the 2.X line—its historical perspective

also makes it relevant to older Pythons that still see regular use today.

Though it’s impossible to predict the future, this book stresses fundamentals that have

been valid for nearly two decades, and will likely apply to future Pythons too. As usual,

I’ll be posting Python updates that impact this book at the book’s website described

ahead. The “What’s New” documents in Python’s manuals set can also serve to fill in

the gaps as Python surely evolves after this book is published.