How to Think Like a Computer Scientist - Learning with Python, 2008a

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15.7 Shuffling the deck 165 >>> deck = Deck() >>> print deck Ace of Clubs 2 of Clubs 3 of Clubs 4 of Clubs 5 of Clubs 6 of Clubs 7 of Clubs 8 of Clubs 9 of Clubs 10 of Clubs Jack of Clubs Queen of Clubs King of Clubs Ace of Diamonds And so on. Even though the result appears on 52 lines, it is one long string that contains newlines. 15.7 Shuffling the deck If a deck is perfectly shuffled, then any card is equally likely to appear anywhere in the deck, and any location in the deck is equally likely to contain any card. To shuffle the deck, we will use the randrange function from the random module. With two integer arguments, a and b, randrange chooses a random integer in the range a
166 Sets of objects class Deck: ... def shuffle(self): import random nCards = len(self.cards) for i in range(nCards): j = random.randrange(i, nCards) self.cards[i], self.cards[j] = self.cards[j], self.cards[i] Rather than assume that there are fifty-two cards in the deck, we get the actual length of the list and store it in nCards. For each card in the deck, we choose a random card from among the cards that haven’t been shuffled yet. Then we swap the current card (i) with the selected card (j). To swap the cards we use a tuple assignment, as in Section 9.2: self.cards[i], self.cards[j] = self.cards[j], self.cards[i] As an exercise, rewrite this line of code without using a sequence assignment. 15.8 Removing and dealing cards Another method that would be useful for the Deck class is removeCard, which takes a card as an argument, removes it, and returns True if the card was in the deck and False otherwise: class Deck: ... def removeCard(self, card): if card in self.cards: self.cards.remove(card) return True else: return False The in operator returns true if the first operand is in the second, which must be a list or a tuple. If the first operand is an object, Python uses the object’s cmp method to determine equality with items in the list. Since the cmp in the Card class checks for deep equality, the removeCard method checks for deep equality. To deal cards, we want to remove and return the top card. The list method pop provides a convenient way to do that:
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How to Think Like a Computer Scient
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How to Think Like a Computer Scient
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Foreword By David Beazley As an edu
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Preface By Jeff Elkner This book ow
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make instant changes whenever someo
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call (type) out its name.” Parame
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Contributor List To paraphrase the
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• Paul Sleigh found an error in C
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xvii • Roger Sperberg pointed out
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Contents Foreword v Preface vii Con
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Contents xxi 4.7 Nested conditional
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Contents xxiii 8.15 Matrices . . .
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Contents xxv 14.4 A more complicate
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Contents xxvii 19.4 Improved Linked
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Chapter 1 The way of the program Th
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1.2 What is a program? 3 $ python P
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1.3 What is debugging? 5 1.3.2 Runt
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1.4 Formal and natural languages 7
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1.6 Glossary 9 source code: A progr
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Chapter 2 Variables, expressions an
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2.3 Variable names and keywords 13
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2.4 Statements 15 >>> 76trombones =
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2.6 Operators and operands 17 2.6 O
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2.9 Composition 19 On one hand, thi
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2.11 Glossary 21 state diagram: A g
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Chapter 3 Functions 3.1 Function ca
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3.4 Math functions 25 >>> minute =
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3.6 Adding new functions 27 problem
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3.7 Definitions and use 29 3.7 Defi
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3.10 Variables and parameters are l
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3.12 Functions with results 33 The
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3.13 Glossary 35 local variable: A
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Chapter 4 Conditionals and recursio
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4.4 Conditional execution 39 In gen
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4.7 Nested conditionals 41 Each con
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4.9 Recursion 43 countdown expects
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4.11 Infinite recursion 45 4.11 Inf
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4.13 Glossary 47 block: A group of
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Chapter 5 Fruitful functions 5.1 Re
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5.2 Program development 51 avoid lo
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5.3 Composition 53 3. Once the prog
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5.5 More recursion 55 But the extra
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5.6 Leap of faith 57 __main__ facto
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5.8 Checking types 59 >>> factorial
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Chapter 6 Iteration 6.1 Multiple as
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6.2 The while statement 63 1. Evalu
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6.3 Tables 65 1.0 0.0 2.0 0.6931471
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6.5 Encapsulation and generalizatio
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6.7 Local variables 69 6.7 Local va
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6.9 Functions 71 the function is ca
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Chapter 7 Strings 7.1 A compound da
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7.3 Traversal and the for loop 75 T
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7.6 Strings are immutable 77 Other
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7.9 The string module 79 As an exer
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7.11 Glossary 81 There are other us
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Chapter 8 Lists A list is an ordere
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8.3 List length 85 If you try to re
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8.6 List operations 87 for VARIABLE
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8.9 List deletion 89 >>> list = [
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8.10 Objects and values 91 8.10 Obj
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8.13 List parameters 93 >>> b[0] =
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8.16 Strings and lists 95 might be
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Chapter 9 Tuples 9.1 Mutability and
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9.3 Tuples as return values 99 9.3
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9.6 Counting 101 >>> randomList(8)
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9.7 Many buckets 103 bucketWidth =
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9.9 Glossary 105 9.9 Glossary Assig
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Chapter 10 Dictionaries The compoun
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10.2 Dictionary methods 109 10.2 Di
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10.5 Hints 111 An alternative is to
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10.6 Long integers 113 Using this v
Page 144 and 145: 10.8 Glossary 115 overflow: A numer
Page 146 and 147: Chapter 11 Files and exceptions Whi
Page 148 and 149: 11.1 Text files 119 The following f
Page 150 and 151: 11.2 Writing variables 121 the str
Page 152 and 153: 11.3 Directories 123 11.3 Directori
Page 154 and 155: 11.5 Exceptions 125 Or trying to op
Page 156 and 157: 11.6 Glossary 127 format sequence:
Page 158 and 159: Chapter 12 Classes and objects 12.1
Page 160 and 161: 12.3 Instances as arguments 131 con
Page 162 and 163: 12.5 Rectangles 133 >>> p1 = Point(
Page 164 and 165: 12.8 Copying 135 The variables dwid
Page 166 and 167: 12.9 Glossary 137 12.9 Glossary cla
Page 168 and 169: Chapter 13 Classes and functions 13
Page 170 and 171: 13.3 Modifiers 141 The output of th
Page 172 and 173: 13.5 Prototype development versus p
Page 174 and 175: 13.8 Glossary 145 Similarly, the te
Page 176 and 177: Chapter 14 Classes and methods 14.1
Page 178 and 179: 14.3 Another example 149 class Time
Page 180 and 181: 14.5 Optional arguments 151 if done
Page 182 and 183: 14.7 Points revisited 153 >>> curre
Page 184 and 185: 14.9 Polymorphism 155 def __mul__(s
Page 186 and 187: 14.10 Glossary 157 Of course, we in
Page 188 and 189: Chapter 15 Sets of objects 15.1 Com
Page 190 and 191: 15.3 Class attributes and the str m
Page 192 and 193: 15.5 Decks 163 def __cmp__(self, ot
Page 196 and 197: 15.9 Glossary 167 class Deck: ... d
Page 198 and 199: Chapter 16 Inheritance 16.1 Inherit
Page 200 and 201: 16.3 Dealing cards 171 16.3 Dealing
Page 202 and 203: 16.6 OldMaidHand class 173 class Ca
Page 204 and 205: 16.7 OldMaidGame class 175 Hand fra
Page 206 and 207: 16.7 OldMaidGame class 177 class Ol
Page 208 and 209: 16.8 Glossary 179 Hand Allen picked
Page 210 and 211: Chapter 17 Linked lists 17.1 Embedd
Page 212 and 213: 17.3 Lists as collections 183 node1
Page 214 and 215: 17.5 Infinite lists 185 We invoke t
Page 216 and 217: 17.8 Wrappers and helpers 187 def r
Page 218 and 219: 17.10 Invariants 189 tail = self.ne
Page 220 and 221: Chapter 18 Stacks 18.1 Abstract dat
Page 222 and 223: 18.4 Pushing and popping 193 def po
Page 224 and 225: 18.7 Evaluating postfix 195 Python
Page 226 and 227: 18.9 Glossary 197 18.9 Glossary abs
Page 228 and 229: Chapter 19 Queues This chapter pres
Page 230 and 231: 19.3 Performance characteristics 20
Page 232 and 233: 19.5 Priority queue 203 and it is m
Page 234 and 235: 19.6 The Golfer class 205 19.6 The
Page 236 and 237: Chapter 20 Trees Like linked lists,
Page 238 and 239: 20.2 Traversing trees 209 20.2 Trav
Page 240 and 241: 20.4 Tree traversal 211 def printTr
Page 242 and 243: 20.5 Building an expression tree 21
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20.5 Building an expression tree 21
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20.7 The animal tree 217 Are you th
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20.8 Glossary 219 def yes(ques): fr
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Appendix A Debugging Different kind
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A.2 Runtime errors 223 A.1.1 I can
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A.2 Runtime errors 225 If there is
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A.3 Semantic errors 227 A.3 Semanti
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A.3 Semantic errors 229 return self
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Appendix B Creating a new data type
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B.1 Fraction multiplication 233 >>>
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B.4 Comparing fractions 235 This re
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B.6 Glossary 237 reduce: To change
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Appendix C Recommendations for furt
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C.2 Recommended general computer sc
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Index Make Way for Ducklings, 75 Py
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Index 245 element, 83, 96 embedded
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Index 247 well-formed, 189 list del
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Index 249 redundancy, 7 reference,
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