第6页 | Learning Python | 阅读 ‧ 电子书库

About This Fourth Edition

This fourth edition of this book has changed in three ways. This edition:

 

Covers both Python 3.0 and Python 2.6—it emphasizes 3.0, but notes differences in 2.6 Includes a set of new chapters mainly targeted at advanced core-language topics Reorganizes some existing material and expands it with new examples for clarity

As I write this edition in 2009, Python comes in two flavors—version 3.0 is an emerging and incompatible mutation of the language, and 2.6 retains backward compatibility with the vast body of existing Python code. Although Python 3 is viewed as the future of Python, Python 2 is still widely used and will be supported in parallel with Python 3 for years to come. While 3.0 is largely the same language, it runs almost no code written for prior releases (the mutation of print from statement to function alone, aesthetically sound as it may be, breaks nearly every Python program ever written).

This split presents a bit of a dilemma for both programmers and book authors. While it would be easier for a book to pretend that Python 2 never existed and cover 3 only, this would not address the needs of the large Python user base that exists today. A vast amount of existing code was written for Python 2, and it won’t be going away any time soon. And while newcomers to the language can focus on Python 3, anyone who must use code written in the past needs to keep one foot in the Python 2 world today. Since it may be years before all third-party libraries and extensions are ported to Python 3, this fork might not be entirely temporary.