Explorations in Computing: An Introduction to Computer Science and Python Programming

435 Pages·2014·15.78 MB·English

by  John S. Conery

Computer Science/Computing
Chapman & Hall/CRC
TEXTBOOKS IN COMPUTING
E
EXPLORATIONS IN COMPUTING
X EXPLORATIONS
An Introduction to Computer Science P
L
and Python Programming IN COMPUTING
O
R
A
Explorations in Computing: An Introduction to Computer Science and Py- An Introduction to Computer Science
T
thon Programming teaches you how to use programming skills to explore
I and Python Programming
fundamental concepts and computational approaches to solving problems. It
O
gives you an introduction to computer science concepts and computer pro-
N
gramming.
S
The text uses Python as the lab software so that you can seamlessly transition

from introductory projects to more advanced studies in later courses. It also I
N
introduces Python programming, providing you with sufficient programming
skills so you can implement your own programs.
C
The interactive lab projects in each chapter allow you to examine important
O
ideas in computer science, particularly how algorithms offer computational
M
solutions to problems. You can type expressions, view results, and run experi-
ments that help you understand the concepts in a hands-on way. The Python P
software modules for each lab project are available on the author’s website. U
Features T
• Emphasizes computational thinking and important concepts in computing I
N
• Gives you sufficient Python programming skills
• Includes tutorial projects that encourage you to explore a particular G
problem and solve it computationally
• Contains standard exercises that test your understanding of the topics
covered
• Provides the software and other ancillaries on the author’s website
Conery
John S. Conery
K16600
K16600_cover.indd 1 7/30/14 12:26 PM

EXPLORATIONS
IN COMPUTING
An Introduction to Computer Science
and Python Programming
K16600_FM.indd 1 8/6/14 11:07 AM
CHAPMAN & HALL/CRC
TEXTBOOKS IN COMPUTING
Series Editors
John Impagliazzo Andrew McGettrick
Professor Emeritus, Hofstra University Department of Computer
and Information Sciences
University of Strathclyde
Aims and Scope

This series covers traditional areas of computing, as well as related technical areas, such as
software engineering, artificial intelligence, computer engineering, information systems, and
information technology. The series will accommodate textbooks for undergraduate and gradu-
ate students, generally adhering to worldwide curriculum standards from professional societ-
ies. The editors wish to encourage new and imaginative ideas and proposals, and are keen to
help and encourage new authors. The editors welcome proposals that: provide groundbreaking
and imaginative perspectives on aspects of computing; present topics in a new and exciting
context; open up opportunities for emerging areas, such as multi-media, security, and mobile
systems; capture new developments and applications in emerging fields of computing; and
address topics that provide support for computing, such as mathematics, statistics, life and
physical sciences, and business.
Published Titles

Paul Anderson, Web 2.0 and Beyond: Principles and Technologies
Henrik Bærbak Christensen, Flexible, Reliable Software: Using Patterns and Agile
Development
John S. Conery, Explorations in Computing: An Introduction to Computer Science
John S. Conery, Explorations in Computing: An Introduction to Computer Science and
Python Programming
Ted Herman, A Functional Start to Computing with Python
Pascal Hitzler, Markus Krötzsch, and Sebastian Rudolph, Foundations of Semantic Web
Technologies
Mark J. Johnson, A Concise Introduction to Data Structures using Java
Mark J. Johnson, A Concise Introduction to Programming in Python
Lisa C. Kaczmarczyk, Computers and Society: Computing for Good
Mark C. Lewis, Introduction to the Art of Programming Using Scala
Bill Manaris and Andrew R. Brown, Making Music with Computers: Creative Programming
in Python
Uvais Qidwai and C.H. Chen, Digital Image Processing: An Algorithmic Approach with
MATLAB®
David D. Riley and Kenny A. Hunt, Computational Thinking for the Modern Problem Solver
Henry M. Walker, The Tao of Computing, Second Edition
K16600_FM.indd 2 8/6/14 11:07 AM
Chapman & Hall/CRC
TEXTBOOKS IN COMPUTING
EXPLORATIONS
IN COMPUTING
An Introduction to Computer Science
and Python Programming
John S. Conery
K16600_FM.indd 3 8/6/14 11:07 AM
CRC Press
Taylor & Francis Group
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Contents
Preface ix
1 Introduction 1
1.1 Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 TheLimitsofComputation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4 ALaboratoryforComputationalExperiments . . . . . . . . . . . . . . . . . . 12
1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 ThePythonWorkbench 17
IntroducingPythonandanenvironmentforinteractiveexperiments
2.1 InteractingwithPython . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2 Numbers,Functions,andtheMathModule. . . . . . . . . . . . . . . . . . . . 24
2.3 Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4 DefiningNewFunctions: defStatements . . . . . . . . . . . . . . . . . . . . . 31
2.5 ConditionalExecution: ifStatements . . . . . . . . . . . . . . . . . . . . . . 36
2.6 Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.7 Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3 TheSieveofEratosthenes 55
Analgorithmforfindingprimenumbers
3.1 TheAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.2 Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3 IteratingOverLists: forStatements . . . . . . . . . . . . . . . . . . . . . . . 62
3.4 ListIndexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.5 TheAnimatedSieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.6 AHelperFunction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.7 The sieve Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.8 (cid:169) RunningaProgramfromtheCommandLine . . . . . . . . . . . . . . . . . 81
3.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
v
vi
4 AJourneyofaThousandMiles 91
Iterationasastrategyforsolvingcomputationalproblems
4.1 TheLinearSearchAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.2 ImplementingLinearSearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.3 TheInsertionSortAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.4 AHelperFunctionforInsertionSort . . . . . . . . . . . . . . . . . . . . . . . 101
4.5 ImplementingInsertionSort . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.6 Scalability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5 DivideandConquer 117
Anewstrategy: Breakinglargeproblemsintosmallersubproblems
5.1 TheBinarySearchAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.2 ImplementingBinarySearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
5.3 BinarySearchExperiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
5.4 TheMergeSortAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.5 ImplementingMergeSort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5.6 MergeSortExperiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
5.7 (cid:169) RecursiveFunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
5.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
6 Spam,Spam,Spam,Mail,andSpam 147
Amachinelearningapproachtofilteringjunkmail
6.1 ACloserLookatStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6.2 ReadingTextfromaFile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
6.3 CountingWordsinaTextFile . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
6.4 Dictionaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
6.5 WordFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
6.6 Spamicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
6.7 AnAlgorithmforIdentifyingJunkMail . . . . . . . . . . . . . . . . . . . . . . 176
6.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
7 NowforSomethingCompletelyDifferent 191
Analgorithmforgeneratingrandomnumbers
7.1 PseudorandomNumbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
7.2 NumbersonDemand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
7.3 ModulesandEncapsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
7.4 GameswithRandomNumbers . . . . . . . . . . . . . . . . . . . . . . . . . . 208
7.5 RandomShuffles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.6 TestsofRandomness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
7.7 DefiningNewObjects: classStatements . . . . . . . . . . . . . . . . . . . . . 224
7.8 (cid:169) AdditionalFeaturesfortheCardClass . . . . . . . . . . . . . . . . . . . . . 234
7.8.1 (cid:169) ClassVariables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
7.8.2 (cid:169) Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
7.8.3 (cid:169) OptionalArguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
7.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
vii
8 BitbyBit 249
Binarycodesandalgorithmsfortextcompressionanderrordetection
8.1 BinaryCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
8.2 CodesforCharacters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
8.3 ErrorDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
8.4 ParityBitsandtheExclusiveOR . . . . . . . . . . . . . . . . . . . . . . . . . . 265
8.5 HuffmanTrees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
8.6 HuffmanCodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
8.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
9 TheWaroftheWords 289
Computerarchitectureandmachinelevelprogramming
9.1 Hello,MARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
9.2 TheTemperatureonMARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
9.3 Corewar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
9.4 Self-ReferentialCode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
9.5 (cid:169) Clones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
9.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
10 I’dLiketoHaveanArgument,Please 315
AprogramthatunderstandsEnglish(ordoesit?)
10.1 OverviewofELIZA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
10.2 SentencePatterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
10.3 BuildingResponsesfromPartsofSentences . . . . . . . . . . . . . . . . . . . 325
10.4 Substitutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
10.5 AnAlgorithmforHavingaConversation . . . . . . . . . . . . . . . . . . . . . 333
10.6 (cid:169) WritingScriptsforELIZA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
10.7 ELIZAandtheTuringTest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
10.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
11 TheMusicoftheSpheres 349
ComputersimulationandtheN-bodyproblem
11.1 RunningAroundinCircles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
11.2 TheForceofGravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
11.3 ForceVectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
11.4 N-BodySimulationoftheSolarSystem . . . . . . . . . . . . . . . . . . . . . . 369
11.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
12 TheTravelingSalesman 379
Ageneticalgorithmforacomputationallydemandingproblem
12.1 MapsandTours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
12.2 ExhaustiveSearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
12.3 RandomSearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
viii
12.4 PointMutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
12.5 TheGeneticAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
12.6 Crossovers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
12.7 (cid:169)TSPHelperFunctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
12.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
Index 417