Chapter 0 Preface 前言

The strange history of this book


In January 1999 I was preparing to teach an introductory programming class in Java. I had taught it three times and I was getting frustrated. The failure rate in the class was too high and, even for students who succeeded, the overall level of achievement was too low.


One of the problems I saw was the books. They were too big, with too much unnecessary detail about Java, and not enough high-level guidance about how to program. And they all suffered from the trap door effect: they would start out easy, proceed gradually, and then somewhere around Chapter 5 the bottom would fall out. The students would get too much new material, too fast, and I would spend the rest of the semester picking up the pieces.


Two weeks before the first day of classes, I decided to write my own book. My goals were:


  • Keep it short. It is better for students to read 10 pages than not read 50 pages.


  • Be careful with vocabulary. I tried to minimize jargon and define each term at first use.


  • Build gradually. To avoid trap doors, I took the most difficult topics and split them into a series of small steps.


  • Focus on programming, not the programming language. I included the minimum useful subset of Java and left out the rest.


I needed a title, so on a whim I chose How to Think Like a Computer Scientist.


My first version was rough, but it worked. Students did the reading, and they understood enough that I could spend class time on the hard topics, the interesting topics and (most important) letting the students practice.


I released the book under the GNU Free Documentation License, which allows users to copy, modify, and distribute the book.


What happened next is the cool part. Jeff Elkner, a high school teacher in Virginia, adopted my book and translated it into Python. He sent me a copy of his translation, and I had the unusual experience of learning Python by reading my own book. As Green Tea Press, I published the first Python version in 2001.

接下来的事情很有趣了。Jeff Elkner,维吉尼亚的一位高中教师,他很欣赏我这本书,把这本书从Java翻译成了Python的版本。他发给我一份『译稿』,然后我开启了阅读『自己的书』来学习Python的奇妙经历。于是在2001年,我通过Green Tea Press出版了本书的第一个Python版本。

In 2003 I started teaching at Olin College and I got to teach Python for the first time. The contrast with Java was striking. Students struggled less, learned more, worked on more interesting projects, and generally had a lot more fun.


Since then I’ve continued to develop the book, correcting errors, improving some of the examples and adding material, especially exercises.


The result is this book, now with the less grandiose title Think Python. Some of the changes are:

  • I added a section about debugging at the end of each chapter. These sections present general techniques for finding and avoiding bugs, and warnings about Python pitfalls.
  • I added more exercises, ranging from short tests of understanding to a few substantial projects. Most exercises include a link to my solution.
  • I added a series of case studies—longer examples with exercises, solutions, and discussion.
  • I expanded the discussion of program development plans and basic design patterns.
  • I added appendices about debugging and analysis of algorithms.

结果就产生了现在这本书,现在标题简化了很多——Think Python。主要的改变如下:

  • 在每一章的末尾,我加了关于debug的部分。这些内容提供了关于debug的一些整体策略,比如如何找到和避免bug,还有就是关于Python一些陷阱进行了提醒。
  • 我加了更多的练习,从简单的理解方面的测试,到一些比较充足的项目。大多数练习都有解决方案的样本链接。
  • 我还添加了一些案例研究,包含练习、解决方案和讨论的更大规模的样例。
  • 此外我还扩展了关于程序开发规划和基本设计模式的讨论。
  • 关于debug和算法分析,还额外加了一些附录。

The second edition of Think Python has these new features:

  • The book and all supporting code have been updated to Python 3.
  • I added a few sections, and more details on the web, to help beginners get started running Python in a browser, so you don’t have to deal with installing Python until you want to.
  • For Chapter 4.1 I switched from my own turtle graphics package, called Swampy, to a more standard Python module, turtle, which is easier to install and more powerful.
  • I added a new chapter called “The Goodies”, which introduces some additional Python features that are not strictly necessary, but sometimes handy.

这本Think Python 的第二版有如下的新内容:

  • 本书内的所有参考代码都升级到Python3了。
  • 我增加了一部分内容,以及一些关于web方面的细节,这是为了帮助初学者能够在浏览器中开始尝试Python,这样即便你不想安装Python也没问题了。
  • 在第四章的第一节,我把我自己的一个原来叫做Swampy的小乌龟图形包转换撑了一个更标准的Python模块,名字叫做turtle,更好安装,功能也比之前强大了。
  • 我还添加了新的一章,叫做『彩蛋』,介绍了一些Python的额外功能,严格来说,这些功能并不算必备的,但有时候蛮好用的。

I hope you enjoy working with this book, and that it helps you learn to program and think like a computer scientist, at least a little bit.


Allen B. Downey

艾伦 唐尼

Olin College




Many thanks to Jeff Elkner, who translated my Java book into Python, which got this project started and introduced me to what has turned out to be my favorite language.

非常感谢Jeff Elkner,是他把我的Java教材翻译成了Python,才引起了这一项目的开始,并且也把Python语言介绍给我,它已经是我最喜欢的编程语言了。

Thanks also to Chris Meyers, who contributed several sections to How to Think Like a Computer Scientist.

也要感谢Chris Meyers,他对『如何像计算机科学家一样思考』的一些章节有贡献。

Thanks to the Free Software Foundation for developing the GNU Free Documentation License, which helped make my collaboration with Jeff and Chris possible, and Creative Commons for the license I am using now.


Thanks to the editors at Lulu who worked on How to Think Like a Computer Scientist.


Thanks to the editors at O’Reilly Media who worked on Think Python.

感谢O’Reilly公司的编辑们,他们出版了这本『Think Python』。

Thanks to all the students who worked with earlier versions of this book and all the contributors (listed below) who sent in corrections and suggestions.


Contributor List


More than 100 sharp-eyed and thoughtful readers have sent in suggestions and corrections over the past few years. Their contributions, and enthusiasm for this project, have been a huge help.


If you have a suggestion or correction, please send email If I make a change based on your feedback, I will add you to the contributor list (unless you ask to be omitted).


If you include at least part of the sentence the error appears in, that makes it easy for me to search. Page and section numbers are fine, too, but not quite as easy to work with. Thanks!



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