Think Python - Denison University

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$Math 232 syllabus - Denison University$

$Math 102 syllabus - Personal Pages - Denison University$

72 Chapter 8. Strings8.2 lenlenisabuilt-infunction that returnsthe number of characters inastring:>>> fruit = 'banana'>>> len(fruit)6To get the lastletter ofastring,you might be tempted totrysomething likethis:>>> length = len(fruit)>>> last = fruit[length]IndexError: string index out of rangeThe reason for the IndexError is that there is no letter in ’banana’ with the index 6. Since westarted counting at zero, the six letters are numbered 0 to 5. To get the last character, you have tosubtract 1 fromlength:>>> last = fruit[length-1]>>> print lastaAlternatively, you can use negative indices, which count backward from the end of the string. Theexpressionfruit[-1]yields the lastletter,fruit[-2]yields thesecond tolast,and soon.8.3 Traversalwith aforloopA lot of computations involve processing a string one character at a time. Often they start at thebeginning, select each character in turn, do something to it, and continue until the end. This patternof processing iscalled atraversal. One way towriteatraversal iswithawhileloop:index = 0while index < len(fruit):letter = fruit[index]print letterindex = index + 1This loop traverses the string and displays each letter on a line by itself. The loop condition isindex < len(fruit), so when index is equal to the length of the string, the condition is false,and the body of the loop is not executed. The last character accessed is the one with the indexlen(fruit)-1,which isthe lastcharacter inthe string.Exercise 8.1 Write a function that takes a string as an argument and displays the letters backward,one per line.Another way towriteatraversal iswithaforloop:for char in fruit:print charEach time through the loop, the next character in the string is assigned to the variable char. Theloop continues untilno characters are left.
8.4. String slices 73Thefollowingexampleshowshowtouseconcatenation(stringaddition)andaforlooptogeneratean abecedarian series (that is, in alphabetical order). In Robert McCloskey’s book Make Way forDucklings,thenamesoftheducklingsareJack,Kack,Lack,Mack,Nack,Ouack,Pack,andQuack.This loop outputs these names inorder:prefixes = 'JKLMNOPQ'suffix = 'ack'for letter in prefixes:print letter + suffixThe output is:JackKackLackMackNackOackPackQackOf course, that’s not quite rightbecause “Ouack” and “Quack” aremisspelled.Exercise 8.2 Modify theprogram tofix thiserror.8.4 StringslicesA segment ofastringiscalled aslice. Selecting asliceissimilartoselecting acharacter:>>> s = 'Monty <strong>Python</strong>'>>> print s[0:5]Monty>>> print s[6:12]<strong>Python</strong>Theoperator[n:m]returnsthepartofthestringfromthe“n-eth”charactertothe“m-eth”character,including the first but excluding the last. This behavior is counterintuitive, but it might help toimagine the indices pointing between thecharacters, as inthe followingdiagram:fruit’ b a n a n a ’index0 1 2 3 4 5 6If you omit the first index (before the colon), the slice starts at the beginning of the string. If youomit thesecond index, theslicegoes tothe end of thestring:>>> fruit = 'banana'>>> fruit[:3]'ban'>>> fruit[3:]'ana'
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Think PythonHowto Think LikeaComput
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Copyright©2008 AllenDowney.Printin
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viChapter 0. PrefaceIn 2003 I start
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viiiChapter 0. Preface• Keith Ver
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xChapter 0. Preface• Patryk Wolow
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xiiContents3 Functions 173.1 Functi
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xivContents7 Iteration 637.1 Multip
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xviContents12 Tuples 11512.1 Tuples
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xviiiContents17 Classes and methods
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xxContents
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2 Chapter 1. The way of theprogramp
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1.4. Formal and natural languages 5
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1.7. Glossary 7Your job is to be a
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Chapter 2Variables,expressions ands
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2.3. Variable names and keywords 11
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2.6. Expressions 132.6 ExpressionsA
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2.10. Debugging 152.10 DebuggingAtt
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Chapter 3Functions3.1 Functioncalls
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3.4. Composition 19>>> math.sqrt(2)
Page 41 and 42: 3.7. Flow of execution 21def repeat
Page 43 and 44: 3.10. Stack diagrams 23Thisfunction
Page 45 and 46: 3.12. Why functions? 253.12 Whyfunc
Page 47 and 48: 3.15. Exercises 27Here’s an examp
Page 49 and 50: Chapter 4Case study: interfacedesig
Page 51 and 52: 4.3. Exercises 31The syntax of a fo
Page 53 and 54: 4.6. Interface design 33This draws
Page 55 and 56: 4.8. A development plan 354.8 Adeve
Page 57 and 58: 4.12. Exercises 37Exercise 4.2 Writ
Page 59 and 60: Chapter 5Conditionals and recursion
Page 61 and 62: 5.5. Alternative execution 41if sta
Page 63 and 64: 5.9. Stack diagrams for recursive f
Page 65 and 66: 5.11. Keyboard input 455.11 Keyboar
Page 67 and 68: 5.14. Exercises 47relational operat
Page 69 and 70: 5.14. Exercises 492. Write a functi
Page 71 and 72: Chapter 6Fruitfulfunctions6.1 Retur
Page 73 and 74: 6.2. Incremental development 53>>>
Page 75 and 76: 6.5. More recursion 55It is common
Page 77 and 78: 6.6. Leap of faith 57__main__factor
Page 79 and 80: 6.9. Debugging 59The first base cas
Page 81 and 82: 6.11. Exercises 61sum = x + y + zpo
Page 83 and 84: Chapter 7Iteration7.1 Multipleassig
Page 85 and 86: 7.4. break 652. Iftheconditionisfal
Page 87 and 88: 7.6. Algorithms 672.00001024003>>>
Page 89 and 90: 7.9. Exercises 69decrement: An upda
Page 91: Chapter 8Strings8.1 Astringis a seq
Page 95 and 96: 8.7. Looping and counting 75This is
Page 97 and 98: 8.10. String comparison 778.10 Stri
Page 99 and 100: 8.12. Glossary 798.12 Glossaryobjec
Page 101 and 102: Chapter 9Case study: word play9.1 R
Page 103 and 104: 9.3. Search 83Exercise 9.6 Write a
Page 105 and 106: 9.5. Debugging 85Here is a version
Page 107 and 108: 9.7. Exercises 87Write a Python pro
Page 109 and 110: Chapter 10Lists10.1 Alist isasequen
Page 111 and 112: 10.3. Traversing alist 9110.3 Trave
Page 113 and 114: 10.7. Map, filter and reduce 93List
Page 115 and 116: 10.9. Listsand strings 95>>> t = ['
Page 117 and 118: 10.12. Listarguments 97The statedia
Page 119 and 120: 10.14. Glossary 99word = word.strip
Page 121 and 122: 10.15. Exercises 101Exercise 10.6 W
Page 123 and 124: Chapter 11DictionariesAdictionaryis
Page 125 and 126: 11.1. Dictionary as asetof counters
Page 127 and 128: 11.4. Dictionaries and lists 107Thi
Page 129 and 130: 11.5. Memos 109corresponding locati
Page 131 and 132: 11.7. Long integers 111count = 0def
Page 133 and 134: 11.10. Exercises 113implementation:
Page 135 and 136: Chapter 12Tuples12.1 Tuples areimmu
Page 137 and 138: 12.3. Tuples as return values 117>>
Page 139 and 140: 12.6. Dictionaries and tuples 119If
Page 141 and 142: 12.7. Comparing tuples 12112.7 Comp
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12.10. Glossary 123>>> t3 = [1, 2,
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Chapter 13Case study: data structur
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13.3. Word histogram 12713.3 Word h
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13.6. Dictionary subtraction 129num
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13.9. Datastructures 131In this tex
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13.11. Glossary 133reading: Examine
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Chapter 14Files14.1 PersistenceMost
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14.4. Filenames and paths 137>>> '%
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14.6. Databases 139Python starts by
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14.9. Writingmodules 141The argumen
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14.11. Glossary 14314.11 Glossarype
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Chapter 15Classes and objects15.1 U
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15.3. Rectangles 147>>> print '(%g,
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15.6. Copying 149>>> print box.widt
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15.8. Glossary 151>>> hasattr(p, 'x
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Chapter 16Classes and functions16.1
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16.3. Modifiers 155if sum.second >=
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16.5. Debugging 157But if we have t
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Chapter 17Classes and methods17.1 O
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17.3. Another example 161Inside the
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17.6. The str method 163>>> time =
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17.9. Polymorphism 165Unfortunately
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17.12. Exercises 167object-oriented
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Chapter 18InheritanceIn this chapte
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18.3. Comparing cards 171Thefirstel
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18.6. Add, remove, shuffle and sort
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18.8. Classdiagrams 175So when you
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18.10. Glossary 177might get the on
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18.11. Exercises 1796. Print a tabl
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Chapter 19Case study: Tkinter19.1 G
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19.3. Canvas widgets 183Exercise 19
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19.6. Packing widgets 185>>> text.i
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19.6. Packing widgets 187self.bu(te
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19.8. Binding 18919.8 BindingAbindi
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19.9. Debugging 19119.9 DebuggingOn
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19.11. Exercises 193image = PIL.ope
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Appendix ADebuggingDifferentkindsof
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A.2. Runtime errors 197A.2 Runtime
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A.3. Semantic errors 199• You are
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A.3. Semantic errors 201The explici
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Indexabecedarian, 72, 83abs functio
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Index 205experimental, 4superstitio
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Index 207raw input, 45recursive, 43
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Index 209map pattern, 93, 100map to
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Index 211poker, 169, 178polygon fun
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Index 213knowing the answer, 53leap
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