Python for software design : how to think like a computer scientist

271 Pages·2009·2.61 MB·English

by  Allen Downey

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Python for Software Design
Python for Software Design is a concise introduction to software design
using the Python programming language. Intended for people with no
programming experience, this book starts with the most basic concepts
and gradually adds new material. Some of the ideas students find most
challenging,likerecursionandobject-orientedprogramming,aredivided
intoasequenceofsmallerstepsandintroducedoverthecourseofseveral
chapters.Thefocusisontheprogrammingprocess,withspecialemphasis
on debugging. The book includes a wide range of exercises, from short
examplestosubstantialprojects,sothatstudentshaveampleopportunity
topracticeeachnewconcept.
ExercisesolutionsandcodeexamplesalongwithSwampy, asuiteof
Pythonprogramsthatisusedinsomeoftheexercises,areavailablefrom
thinkpython.com.
Allen B. Downey, Ph.D., is an Associate Professor of Computer Sci-
enceattheOlinCollegeofEngineeringinNeedham,Massachusetts.He
has taught at Wellesley College, Colby College, and UC Berkeley. He
has a doctorate in computer science from UC Berkeley and a master’s
degreefromMIT.ProfessorDowneyistheauthorofapreviousversion
ofthisbook,titledHowtoThinkLikeaComputerScientist:Learningwith
Python,whichheself-publishedin2001.

PYTHON FOR
SOFTWARE
DESIGN
How to Think Like a
Computer Scientist
Allen B. Downey
OlinCollegeofEngineering
CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo
Cambridge University Press
The Edinburgh Building, Cambridge CB2 8RU, UK
Published in the United States of America by Cambridge University Press, New York
www.cambridge.org
Information on this title: www.cambridge.org/9780521898119
© Allen B. Downey 2009
This publication is in copyright. Subject to statutory exception and to the
provision of relevant collective licensing agreements, no reproduction of any part
may take place without the written permission of Cambridge University Press.
First published in print format 2009
ISBN-13 978-0-511-50731-1 eBook (EBL)
ISBN-13 978-0-521-89811-9 hardback
ISBN-13 978-0-521-72596-5 paperback
Cambridge University Press has no responsibility for the persistence or accuracy
of urls for external or third-party internet websites referred to in this publication,
and does not guarantee that any content on such websites is, or will remain,
accurate or appropriate.
Contents
Preface page xi
1 The Way of the Program 1
1.1 ThePythonProgrammingLanguage 1
1.2 WhatIsaProgram? 3
1.3 WhatIsDebugging? 3
1.3.1 SyntaxErrors 3
1.3.2 RuntimeErrors 4
1.3.3 SemanticErrors 4
1.3.4 ExperimentalDebugging 4
1.4 FormalandNaturalLanguages 5
1.5 TheFirstProgram 6
1.6 Debugging 7
1.7 Glossary 8
1.8 Exercises 9
2 Variables, Expressions, and Statements 10
2.1 ValuesandTypes 10
2.2 Variables 11
2.3 VariableNamesandKeywords 13
2.4 Statements 13
2.5 OperatorsandOperands 14
2.6 Expressions 15
2.7 OrderofOperations 15
2.8 StringOperations 16
2.9 Comments 17
2.10 Debugging 17
2.11 Glossary 18
2.12 Exercises 19
v
vi Contents
3 Functions 21
3.1 FunctionCalls 21
3.2 TypeConversionFunctions 21
3.3 MathFunctions 22
3.4 Composition 23
3.5 AddingNewFunctions 24
3.6 DefinitionsandUses 26
3.7 FlowofExecution 26
3.8 ParametersandArguments 27
3.9 VariablesandParametersAreLocal 28
3.10 StackDiagrams 29
3.11 FruitfulFunctionsandVoidFunctions 30
3.12 WhyFunctions? 31
3.13 Debugging 31
3.14 Glossary 32
3.15 Exercises 33
4 Case Study: Interface Design 35
4.1 TurtleWorld 35
4.2 SimpleRepetition 36
4.3 Exercises 37
4.4 Encapsulation 38
4.5 Generalization 39
4.6 InterfaceDesign 40
4.7 Refactoring 41
4.8 ADevelopmentPlan 42
4.9 Docstring 43
4.10 Debugging 43
4.11 Glossary 44
4.12 Exercises 44
5 Conditionals and Recursion 46
5.1 ModulusOperator 46
5.2 BooleanExpressions 46
5.3 LogicalOperators 47
5.4 ConditionalExecution 48
5.5 AlternativeExecution 48
5.6 ChainedConditionals 49
5.7 NestedConditionals 49
5.8 Recursion 50
5.9 StackDiagramsforRecursiveFunctions 52
5.10 InfiniteRecursion 52
5.11 KeyboardInput 53
5.12 Debugging 54
5.13 Glossary 55
5.14 Exercises 56
Contents vii
6 Fruitful Functions 59
6.1 ReturnValues 59
6.2 IncrementalDevelopment 60
6.3 Composition 63
6.4 BooleanFunctions 64
6.5 MoreRecursion 65
6.6 LeapofFaith 67
6.7 OneMoreExample 67
6.8 CheckingTypes 68
6.9 Debugging 69
6.10 Glossary 70
6.11 Exercises 71
7 Iteration 73
7.1 MultipleAssignment 73
7.2 UpdatingVariables 74
7.3 ThewhileStatement 75
7.4 break 76
7.5 SquareRoots 77
7.6 Algorithms 79
7.7 Debugging 79
7.8 Glossary 80
7.9 Exercises 80
8 Strings 82
8.1 AStringIsaSequence 82
8.2 len 83
8.3 TraversalwithaforLoop 83
8.4 StringSlices 85
8.5 StringsAreImmutable 86
8.6 Searching 86
8.7 LoopingandCounting 87
8.8 stringMethods 87
8.9 TheinOperator 89
8.10 StringComparison 89
8.11 Debugging 90
8.12 Glossary 92
8.13 Exercises 92
9 Case Study: Word Play 95
9.1 ReadingWordLists 95
9.2 Exercises 96
9.3 Search 97
9.4 LoopingwithIndices 99
9.5 Debugging 100
9.6 Glossary 101
9.7 Exercises 101
viii Contents
10 Lists 103
10.1 AListIsaSequence 103
10.2 ListsAreMutable 104
10.3 TraversingaList 105
10.4 ListOperations 106
10.5 ListSlices 106
10.6 ListMethods 107
10.7 Map,Filter,andReduce 108
10.8 DeletingElements 109
10.9 ListsandStrings 110
10.10 ObjectsandValues 111
10.11 Aliasing 113
10.12 ListArguments 113
10.13 Debugging 115
10.14 Glossary 116
10.15 Exercises 117
11 Dictionaries 119
11.1 DictionaryasaSetofCounters 121
11.2 LoopingandDictionaries 123
11.3 ReverseLookup 123
11.4 DictionariesandLists 124
11.5 Memos 126
11.6 GlobalVariables 128
11.7 LongIntegers 129
11.8 Debugging 130
11.9 Glossary 131
11.10 Exercises 131
12 Tuples 133
12.1 TuplesAreImmutable 133
12.2 TupleAssignment 135
12.3 TuplesasReturnValues 136
12.4 Variable-LengthArgumentTuples 136
12.5 ListsandTuples 138
12.6 DictionariesandTuples 139
12.7 ComparingTuples 141
12.8 SequencesofSequences 142
12.9 Debugging 143
12.10 Glossary 144
12.11 Exercises 145
13 Case Study: Data Structure Selection 147
13.1 WordFrequencyAnalysis 147
13.2 RandomNumbers 148
13.3 WordHistogram 149
13.4 MostCommonWords 151