How to Think Like a Computer Scientist
Learning with Python
ii
How to Think Like a Computer Scientist
Learning with Python
Allen Downey
Jeffrey Elkner
Chris Meyers
Green Tea Press
Wellesley, Massachusetts
Copyright
c
2002 Allen Downey, Jeffrey Elkner, and Chris Meyers.
Edited by Shannon Turlington and Lisa Cutler. Cover design by Rebecca Gimenez.
Printing history:
April 2002: First edition.
August 2008: Second printing.
Green Tea Press
1 Grove St.
P.O. Box 812901
Wellesley, MA 02482
Permission is granted to copy, distribute, and/or modify this document under the terms
of the GNU Free Documentation License, Version 1.1 or any later version published by
the Free Software Foundation; with the Invariant Sections being “Foreword,” “Preface,”
and “Contributor List,” with no Front-Cover Texts, and with no Back-Cover Texts.
A copy of the license is included in the appendix entitled “GNU Free Documentation
License.”
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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Publisher’s Cataloging-in-Publication (provided by Quality Books, Inc.)
Downey, A llen
How to think like a computer scientist : learning
with Python / Allen Downey, Jeffrey Elkner, Chr is
Meyers. – 1st ed.
p. cm.
Includes index.
ISBN 0-9716775-0-6
LCCN 2002100618
1. Python (Computer program language) I. Elkner,
Jeffrey. II. Meyers, Chris. I II. Title
QA76.73.P98D69 2002 005.13’3
QBI02-200031
Foreword
By David Beazley
As an educator, researcher, and book author, I am delighted to see the completion
of this book. Python is a fun and extremely easy-to-use programming language
that has steadily gained in popularity over the last few years. Developed over
ten years ago by Guido van Rossum, Python’s simple syntax and overall feel is
largely derived from ABC, a teaching language that was developed in the 1980’s.
However, Python was also created to solve real problems and it borrows a wide
variety of features from programming languages such as C++, Java, Modula-3,
and Scheme. Because of this, one of Python’s most remarkable features is its
broad appeal to professional software developers, scientists, researchers, artists,
and educators.
Despite Python’s appeal to many different communities, you may still wonder
“why Python?” or “why teach programming with Python?” Answering these
questions is no simple task—especially when popular opinion is on the side of
more masochistic alternatives such as C++ and Java. However, I think the most
direct answer is that programming in Python is simply a lot of fun and more
productive.
When I teach computer science courses, I want to cover important concepts in
addition to making the material interesting and engaging to students. Unfortu-
nately, there is a tendency for introductory programming courses to focus far too
much attention on mathematical abstraction and for s tudents to become frus-
trated with annoying problems related to low-level details of syntax, compilation,
and the enforcement of seemingly arcane rules. Although such abstraction and
formalism is imp ortant to professional software engineers and students who plan
to continue their study of computer science, taking such an approach in an intro-
ductory course mostly succeeds in making computer science boring. When I teach
a course, I don’t want to have a room of uninspired students. I would much rather
see them trying to solve interesting problems by exploring different ideas, taking
unconventional approaches, breaking the rules, and learning from their mistakes.
