Learning Python - Mark Lutz [7]
Whether you are new to programming or are a professional developer, this book’s goal is to bring you quickly up to speed on the fundamentals of the core Python language. After reading this book, you will know enough about Python to apply it in whatever application domains you choose to explore.
By design, this book is a tutorial that focuses on the core Python language itself, rather than specific applications of it. As such, it’s intended to serve as the first in a two-volume set:
Learning Python, this book, teaches Python itself.
Programming Python, among others, shows what you can do with Python after you’ve learned it.
That is, applications-focused books such as Programming Python pick up where this book leaves off, exploring Python’s role in common domains such as the Web, graphical user interfaces (GUIs), and databases. In addition, the book Python Pocket Reference provides additional reference materials not included here, and it is designed to supplement this book.
Because of this book’s foundations focus, though, it is able to present Python fundamentals with more depth than many programmers see when first learning the language. And because it’s based upon a three-day Python training class with quizzes and exercises throughout, this book serves as a self-paced introduction to the language.
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.
Coverage for Both 3.0 and 2.6
To address this dichotomy and to meet the needs of all potential readers, this edition of this book has been updated to cover both Python 3.0 and Python 2.6 (and later releases in the 3.X and 2.X lines). It’s intended for programmers using Python 2, programmers using Python 3, and programmers stuck somewhere between the two.
That is, you can use this book to learn either Python line. Although the focus here is on 3.0 primarily, 2.6 differences and tools are also noted along the way for programmers using older code. While the two versions are largely the same, they diverge in some important ways, and I’ll point these out along the way.
For instance, I’ll use 3.0 print calls in most examples, but will describe the 2.6 print statement, too, so you can make sense of earlier code. I’ll also