Think Python (pdf) - Green Tea Press

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.
Thanks also to Chris Meyers, who contributed several sections toHow to Think Like a Com-
puter Scientist.
Thanks to the Free Software Foundation for developing the GNU Free Documentation Li-
cense, which helped make my collaboration with Jeff and Chris possible, and Creative
Commons for the license I am using now.
vii
Thanks to the editors at Lulu who worked onHow to Think Like a Computer Scientist.
Thanks to the editors at O"Reilly Media who worked onThink Python.
Thanks to all the students who worked with earlier versions of this book and all the con-
tributors (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 to????????????????????????.
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!
• Lloyd Hugh Allen sent in a correction to Section 8.4.
• Yvon Boulianne sent in a correction of a semantic error in Chapter 5.
• Fred Bremmer submitted a correction in Section 2.1.
• Jonah Cohen wrote the Perl scripts to convert the LaTeX source for this book into beautiful
HTML.
• Michael Conlon sent in a grammar correction in Chapter 2 and an improvement in style in
Chapter 1, and he initiated discussion on the technical aspects of interpreters.
• Benoît Girard sent in a correction to a humorous mistake in Section 5.6.
• Courtney Gleason and Katherine Smith wrote???????????, which was used as a case study
in an earlier version of the book. Their program can now be found on the website.
• Lee Harr submitted more corrections than we have room to list here, and indeed he should be
listed as one of the principal editors of the text.
• James Kaylin is a student using the text. He has submitted numerous corrections.
• David Kershaw fixed the broken????????function in Section 3.10.
• Eddie Lam has sent in numerous corrections to Chapters 1, 2, and 3. He also fixed the Makefile
so that it creates an index the first time it is run and helped us set up a versioning scheme.
• Man-Yong Lee sent in a correction to the example code in Section 2.4.
• David Mayo pointed out that the word "unconsciously" in Chapter 1 needed to be changed to
"subconsciously".
• Chris McAloon sent in several corrections to Sections 3.9 and 3.10.
• Matthew J. Moelter has been a long-time contributor who sent in numerous corrections and
suggestions to the book.
viii Chapter 0. Preface
• Simon Dicon Montford reported a missing function definition and several typos in Chapter 3.
He also found errors in the?????????function in Chapter 13.
• John Ouzts corrected the definition of "return value" in Chapter 3.
• Kevin Parks sent in valuable comments and suggestions as to how to improve the distribution
of the book.
• David Pool sent in a typo in the glossary of Chapter 1, as well as kind words of encouragement.
• Michael Schmitt sent in a correction to the chapter on files and exceptions.
• Robin Shaw pointed out an error in Section 13.1, where the printTime function was used in an
example without being defined.
• Paul Sleigh found an error in Chapter 7 and a bug in Jonah Cohen"s Perl script that generates
HTML from LaTeX.
• Craig T. Snydal is testing the text in a course at Drew University. He has contributed several
valuable suggestions and corrections.
• IanThomasandhisstudentsareusingthetextinaprogrammingcourse. Theyarethefirstones
to test the chapters in the latter half of the book, and they have made numerous corrections and
suggestions.
• Keith Verheyden sent in a correction in Chapter 3.
• Peter Winstanley let us know about a longstanding error in our Latin in Chapter 3.
• Chris Wrobel made corrections to the code in the chapter on file I/O and exceptions.
• Moshe Zadka has made invaluable contributions to this project. In addition to writing the first
draft of the chapter on Dictionaries, he provided continual guidance in the early stages of the
book.
• Christoph Zwerschke sent several corrections and pedagogic suggestions, and explained the
difference betweengleichandselbe.
• James Mayer sent us a whole slew of spelling and typographical errors, including two in the
contributor list.
• Hayden McAfee caught a potentially confusing inconsistency between two examples.
• Angel Arnal is part of an international team of translators working on the Spanish version of
the text. He has also found several errors in the English version.
• Tauhidul Hoque and Lex Berezhny created the illustrations in Chapter 1 and improved many
of the other illustrations.
• Dr. Michele Alzetta caught an error in Chapter 8 and sent some interesting pedagogic com-
ments and suggestions about Fibonacci and Old Maid.
• Andy Mitchell caught a typo in Chapter 1 and a broken example in Chapter 2.
• Kalin Harvey suggested a clarification in Chapter 7 and caught some typos.
• Christopher P. Smith caught several typos and helped us update the book for Python 2.2.
• David Hutchins caught a typo in the Foreword.
• Gregor Lingl is teaching Python at a high school in Vienna, Austria. He is working on a Ger-
man translation of the book, and he caught a couple of bad errors in Chapter 5.
ix
• Julie Peters caught a typo in the Preface.
• Florin Oprina sent in an improvement in????????, a correction in?????????, and a nice typo.
• D. J. Webre suggested a clarification in Chapter 3.
• Ken found a fistful of errors in Chapters 8, 9 and 11.
• Ivo Wever caught a typo in Chapter 5 and suggested a clarification in Chapter 3.
• Curtis Yanko suggested a clarification in Chapter 2.
• Ben Logan sent in a number of typos and problems with translating the book into HTML.
• Jason Armstrong saw the missing word in Chapter 2.
• Louis Cordier noticed a spot in Chapter 16 where the code didn"t match the text.
• Brian Cain suggested several clarifications in Chapters 2 and 3.
• Rob Black sent in a passel of corrections, including some changes for Python 2.2.
• Jean-Philippe Rey at École Centrale Paris sent a number of patches, including some updates
for Python 2.2 and other thoughtful improvements.
• Jason Mader at George Washington University made a number of useful suggestions and cor-
rections.
• Jan Gundtofte-Bruun reminded us that "a error" is an error.
• Abel David and Alexis Dinno reminded us that the plural of "matrix" is "matrices", not "ma-
trixes". This error was in the book for years, but two readers with the same initials reported it
on the same day. Weird.
• Charles Thayer encouraged us to get rid of the semi-colons we had put at the ends of some
statements and to clean up our use of "argument" and "parameter".
• Roger Sperberg pointed out a twisted piece of logic in Chapter 3.
• Sam Bull pointed out a confusing paragraph in Chapter 2.
• Andrew Cheung pointed out two instances of "use before def".
• C. Corey Capel spotted the missing word in the Third Theorem of Debugging and a typo in
Chapter 4.
• Alessandra helped clear up some Turtle confusion.
• Wim Champagne found a brain-o in a dictionary example.
• Douglas Wright pointed out a problem with floor division in???.
• Jared Spindor found some jetsam at the end of a sentence.
• Lin Peiheng sent a number of very helpful suggestions.
• Ray Hagtvedt sent in two errors and a not-quite-error.
• Torsten Hübsch pointed out an inconsistency in Swampy.
• Inga Petuhhov corrected an example in Chapter 14.
• Arne Babenhauserheide sent several helpful corrections.
x Chapter 0. Preface
• Mark E. Casida is is good at spotting repeated words.
• Scott Tyler filled in a that was missing. And then sent in a heap of corrections.
• Gordon Shephard sent in several corrections, all in separate emails.
• Andrew Turner????ted an error in Chapter 8.
• Adam Hobart fixed a problem with floor division in???.
• Daryl Hammond and Sarah Zimmerman pointed out that I served up???????too early. And
Zim spotted a typo.
• George Sass found a bug in a Debugging section.
• Brian Bingham suggested Exercise 11.5.
• Leah Engelbert-Fenton pointed out that I used?????as a variable name, contrary to my own
advice. And then found a bunch of typos and a "use before def".
• Joe Funke spotted a typo.
• Chao-chao Chen found an inconsistency in the Fibonacci example.
• Jeff Paine knows the difference between space and spam.
• Lubos Pintes sent in a typo.
• Gregg Lind and Abigail Heithoff suggested Exercise 14.3.
• Max Hailperin has sent in a number of corrections and suggestions. Max is one of the authors
of the extraordinaryConcrete Abstractions, which you might want to read when you are done
with this book.
• Chotipat Pornavalai found an error in an error message.
• Stanislaw Antol sent a list of very helpful suggestions.
• Eric Pashman sent a number of corrections for Chapters 4-11.
• Miguel Azevedo found some typos.
• Jianhua Liu sent in a long list of corrections.
• Nick King found a missing word.
• Martin Zuther sent a long list of suggestions.
• Adam Zimmerman found an inconsistency in my instance of an "instance" and several other
errors.