Learning Python - Mark Lutz [8]
If you are learning Python for the first time and don’t need to use any legacy code, I encourage you to begin with Python 3.0; it cleans up some longstanding warts in the language, while retaining all the original core ideas and adding some nice new tools. Many popular Python libraries and tools will likely be available for Python 3.0 by the time you read these words, especially given the file I/O performance improvements expected in the upcoming 3.1 release. If you are using a system based on Python 2.X, however, you’ll find that this book addresses your concerns, too, and will help you migrate to 3.0 in the future.
By proxy, this edition addresses other Python version 2 and 3 releases as well, though some older version 2.X code may not be able to run all the examples here. Although class decorators are available in both Python 2.6 and 3.0, for example, you cannot use them in an older Python 2.X that did not yet have this feature. See Tables 1 and 2 later in this Preface for summaries of 2.6 and 3.0 changes.
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Note
Shortly before going to press, this book was also augmented with notes about prominent extensions in the upcoming Python 3.1 release—comma separators and automatic field numbering in string format method calls, multiple context manager syntax in with statements, new methods for numbers, and so on. Because Python 3.1 was targeted primarily at optimization, this book applies directly to this new release as well. In fact, because Python 3.1 supersedes 3.0, and because the latest Python is usually the best Python to fetch and use anyhow, in this book the term “Python 3.0” generally refers to the language variations introduced by Python 3.0 but that are present in the entire 3.X line.
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New Chapters
Although the main purpose of this edition is to update the examples and material from the preceding edition for 3.0 and 2.6, I’ve also added five new chapters to address new topics and add context:
Chapter 27 is a new class tutorial, using a more realistic example to explore the basics of Python object-oriented programming (OOP).
Chapter 36 provides details on Unicode and byte strings and outlines string and file differences between 3.0 and 2.6.
Chapter 37 collects managed attribute tools such as properties and provides new coverage of descriptors.
Chapter 38 presents function and class decorators and works through comprehensive examples.
Chapter 39 covers metaclasses and compares and contrasts them with decorators.
The first of these chapters provides a gradual, step-by-step tutorial for using classes and OOP in Python. It’s based upon a live demonstration I have been using in recent years in the training classes I teach, but has been honed here for use in a book. The chapter is designed to show OOP in a more realistic context than earlier examples and to illustrate how class concepts come together into larger, working programs. I hope it works as well here as it has in live classes.
The last four of these new chapters are collected in a new final part of the book, “Advanced Topics.” Although these are technically core language topics, not every Python programmer needs to delve into the details of Unicode text or metaclasses. Because of this, these four chapters have been separated out into this new part, and are officially optional reading. The details of Unicode and binary data strings, for example, have been moved to this final part because most programmers use simple ASCII strings and don’t need to know about these topics. Similarly, decorators and metaclasses are specialist topics that are usually of more interest to API builders than application programmers.
If you do use such tools, though, or use code that does, these new advanced topic chapters should help you master the basics. In addition, these chapters’ examples include case studies that tie core language concepts together,