Introduction

This book is intended to be a concise reference to the Python programming language. Although an experienced programmer will probably be able to learn Python from this book, it’s not intended to be an extended tutorial or a treatise on how to program. Rather, the goal is to present the core Python language, and the most essential parts of the Python library in a manner that’s accurate and concise. This book assumes that the reader has prior programming experience with Python or another language such as C or Java. In addition, a general familiarity with systems programming topics (for example, basic operating system concepts and network programming) may be useful in understanding certain parts of the library reference.

Python is freely available for download at http://www.python.org. Versions are available for almost every operating system, including UNIX, Windows, and Macintosh. In addition, the Python website includes links to documentation, how-to guides, and a wide assortment of third-party software.

This edition of Python Essential Reference comes at a pivotal time in Python’s evolution. Python 2.6 and Python 3.0 are being released almost simultaneously. Yet, Python 3 is a release that breaks backwards compatibility with prior Python versions. As an author and programmer, I’m faced with a dilemma: do I simply jump forward to Python 3.0 or do I build upon the Python 2.x releases that are more familiar to most programmers?

Years ago, as a C programmer I used to treat certain books as the ultimate authority on what programming language features should be used. For example, if you were using something that wasn’t documented in the K&R book, it probably wasn’t going to be portable and should be approached with caution. This approach served me very well as a programmer and it’s the approach I have decided to take in this edition of the Essential Reference. Namely, I have chosen to omit features of Python 2 that have been removed from Python 3. Likewise, I don’t focus on features of Python 3 that have not been back-ported (although such features are still covered in an appendix). As a result, I hope this book can be a useful companion for Python programmers, regardless of what Python version is being used.

The fourth edition of Python Essential Reference also includes some of the most exciting changes since its initial publication nearly ten years ago. Much of Python’s development throughout the last few years has focused on new programming language features—especially related to functional and meta programming. As a result, the chapters on functions and object-oriented programming have been greatly expanded to cover topics such as generators, iterators, coroutines, decorators, and metaclasses. The library chapters have been updated to focus on more modern modules. Examples and code fragments have also been updated throughout the book. I think most programmers will be quite pleased with the expanded coverage.

Finally, it should be noted that Python already includes thousands of pages of useful documentation. The contents of this book are largely based on that documentation, but with a number of key differences. First, this reference presents information in a much more compact form, with different examples and alternative descriptions of many topics. Second, a significant number of topics in the library reference have been expanded to include outside reference material. This is especially true for low-level system and networking modules in which effective use of a module normally relies on a myriad of options listed in manuals and outside references. In addition, in order to produce a more concise reference, a number of deprecated and relatively obscure library modules have been omitted.

In writing this book, it has been my goal to produce a reference containing virtually everything I have needed to use Python and its large collection of modules. Although this is by no means a gentle introduction to the Python language, I hope that you find the contents of this book to be a useful addition to your programming reference library for many years to come. I welcome your comments.

      David Beazley
      Chicago, Illinois
      June, 2009