Think Python
How to Think Like a Computer Scientist
Version 1.1.20
Think Python
How to Think Like a Computer Scientist
Version 1.1.20
Allen Downey
Green Tea Press
Needham, Massachusetts
Copyright © 2008 Allen Downey.
Printing history:
April 2002: First edition of How to Think Like a Computer Scientist.
Augus t 2007: Major revision, changed title to How to Think Like a (Python) Programmer.
June 2008: Major revision, changed title to Think Python: How to Think Like a Computer Scientist.
Green Tea Press
9 Washburn Ave
Needham MA 02492
Permission is granted to copy, distribute, and/or modify this document under the terms of the GNU Free Doc-
umentation License, Version 1.1 or any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and with no Back-Cover Texts.
The GNU Free Documentation License is available from
www.gnu.org
or by writing to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
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The L
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http://www.thinkpython.com
Preface
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 the 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 J ava 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 distr ibute the book.
What happened next is the cool part. Jeff Elkner, a high school t eacher 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 l earning Python by reading my own book.
Jeff and I revised the book, incorporated a case study by Chris Meyers, and in 2001 we released
How to Think Like a Computer Scientist: Learning with Python, also under the GNU Free Doc-
umentation License. As Green Tea Press, I published the book and started selling hard copies
through Amazon.com and college book stores. Other books from Green Tea Press are available at
greenteapress.com
.
