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Invent Your Own Computer Games with Python, 4th edition

Invent Your Own Computer Games with Python, 4th edition

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by Al Sweigart

Brief Contents

The Interactive Shell
Writing Programs
Guess the Number
A Joke-Telling Program 
Dragon Realm
Using the Debugger 
Designing Hangman with Flowcharts
Writing the Hangman Code
Extending Hangman
Tic-Tac-Toe
The Bagels Deduction Game 
The Cartesian Coordinate System
Sonar Treasure Hunt
Caesar Cipher 
The Reversegam Game
Reversegam AI Simulation
Creating Graphics
Animating Graphics
Collision Detection
Using Sounds and Images
A Dodger Game with Sounds and Images

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Book Details
 Price
 3.00 USD
 Pages
 374 p
 File Size
 8,623 KB
 File Type
 PDF format
 ISBN-10
 ISBN-13
 1-59327-795-4
 978-1-59327-795-6 
 Copyright   
 2017 by Al Sweigart 

About the Author
Al Sweigart is a software developer, tech book author, and hoopy frood
who really knows where his towel is. He has written several programming
books for beginners, including Automate the Boring Stuff with Python and
Scratch Programming Playground, also from No Starch Press. 
His books are freely available under a Creative Commons license at his website https://inventwithpython.com/.

About the Technical Reviewer
Ari Lacenski is a developer of Android applications and Python software.
She lives in the Bay Area, where she writes about Android programming at
http://gradlewhy.ghost.io/ and mentors with Women Who Code.

Introduction
When I first played video games as a kid,
I was hooked. But I didn’t just want to
play video games, I wanted to make them.
I found a book like this one that taught me
how to write my first programs and games. It was fun
and easy. The first games I made were like the ones
in this book. They weren’t as fancy as the Nintendo
games my parents bought for me, but they were games
I had made myself.
Now, as an adult, I still have fun programming and I get paid for it. But
even if you don’t want to become a computer programmer, programming
is a useful and fun skill to have. It trains your brain to think logically, make
plans, and reconsider your ideas whenever you find mistakes in your code.

Many programming books for beginners fall into two categories. The
first category includes books that don’t teach programming so much as
“game creation software” or languages that simplify so much that what is
taught is no longer programming. The other category consists of books
that teach programming like a mathematics textbook—all principles and
concepts, with few real-life applications for the reader. This book takes
a different approach and teaches you how to program by making video
games. I show the source code for the games right up front and explain
programming principles from the examples. This approach was the key
for me when I was learning to program. The more I learned how other
people’s programs worked, the more ideas I had for my own programs.
All you’ll need is a computer, some free software called the Python
interpreter, and this book. Once you learn how to create the games in this
book, you’ll be able to develop games on your own.

Computers are incredible machines, and learning to program them
isn’t as hard as people think. A computer program is a bunch of instructions
that the computer can understand, just like a storybook is a bunch of sentences
that the reader can understand. To instruct a computer, you write a
program in a language the computer understands. This book will teach you
a programming language called Python. There are many other programming
languages you can learn, like BASIC, Java, JavaScript, PHP, and C++.
When I was a kid, I learned BASIC, but newer programming languages
like Python are even easier to learn. Python is also used by professional programmers
in their work and when programming for fun. Plus it’s totally free
to install and use—you’ll just need an internet connection to download it.

Because video games are nothing but computer programs, they are
also made up of instructions. The games you’ll create from this book seem
simple compared to the games for Xbox, PlayStation, or Nintendo. These
games don’t have fancy graphics because they’re meant to teach you coding
basics. They’re purposely simple so you can focus on learning to program.
Games don’t have to be complicated to be fun!

Table of Contents
Acknowledgments xix
Introduction xxi
Who Is This Book For? xxii
About This Book xxiii
How to Use This Book xxiv
Line Numbers and Indentation . xxiv
Long Code Lines xxv
Downloading and Installing Python . xxv
Starting IDLE . xxvi
Finding Help Online xxvii
1 The Interactive Shell 1
Some Simple Math 2
Integers and Floating-Point Numbers . 2
Expressions . 3
Evaluating Expressions . 3
Syntax Errors 4
Storing Values in Variables 5
Summary . 8
2 Writing Programs 11
String Values 12
String Concatenation . 13
Writing Programs in IDLE’s File Editor 13
Creating the Hello World Program . 14
Saving Your Program 15
Running Your Program 16
How the Hello World Program Works . 17
Comments for the Programmer . 17
Functions: Mini-Programs Inside Programs . 18
The End of the Program   19
Naming Variables . 20
Summary . 20
3 Guess the Number 21
Sample Run of Guess the Number . 22
Source Code for Guess the Number 22
Importing the random Module  23
Generating Random Numbers with the random.randint() Function . 24
Welcoming the Player . 26
Flow Control Statements . 26
Using Loops to Repeat Code 26
Grouping with Blocks . 27
Looping with for Statements . 28
Getting the Player’s Guess 29
Converting Values with the int(), float(), and str() Functions . 29
The Boolean Data Type 31
Comparison Operators . 32
Checking for True or False with Conditions 32
Experimenting with Booleans, Comparison Operators, and Conditions . 33
The Difference Between = and == 34
if Statements . 34
Leaving Loops Early with the break Statement . 35
Checking Whether the Player Won . 35
Checking Whether the Player Lost . 35
Summary . 36
4 A Joke-Telling Program 39
Sample Run of Jokes 40
Source Code for Jokes . 40
How the Code Works 41
Escape Characters 41
Single and Double Quotes . 42
The print() Function’s end Keyword Parameter . 43
Summary . 44
5 Dragon Realm 45
How to Play Dragon Realm 45
Sample Run of Dragon Realm . 46
Flowchart for Dragon Realm . 46
Source Code for Dragon Realm 47
Importing the random and time Modules 48
Functions in Dragon Realm . 49
def Statements . 49
Calling a Function 49
Where to Put Function Definitions . 50
Multiline Strings 50
How to Loop with while Statements . 51
Boolean Operators 52
The and Operator 52
The or Operator . 53
The not Operator . 53
Evaluating Boolean Operators . 54
Return Values 55
Global Scope and Local Scope . 56
Function Parameters 57
Displaying the Game Results  58
Deciding Which Cave Has the Friendly Dragon 59
The Game Loop 60
Calling the Functions in the Program . 60
Asking the Player to Play Again . 61
Summary . 61
6 Using the Debugger 63
Types of Bugs . 64
The Debugger . 65
Starting the Debugger . 65
Stepping Through the Program with the Debugger 67
Finding the Bug  70
Setting Breakpoints 73
Using Breakpoints . 73
Summary . 75
7 Designing Hangman with Flowcharts 77
How to Play Hangman . 78
Sample Run of Hangman . 78
ASCII Art . 79
Designing a Program with a Flowchart 80
Creating the Flowchart 81
Branching from a Flowchart Box 81
Ending or Restarting the Game 83
Guessing Again . 83
Offering Feedback to the Player . 85
Summary . 86
8 Writing the Hangman Code 87
Source Code for Hangman  88
Importing the random Module   91
Constant Variables 91
The Lists Data Type 92
Accessing Items with Indexes . 92
List Concatenation 94
The in Operator . 94
Calling Methods . 94
The reverse() and append() List Methods . 95
The split() String Method . 95
Getting a Secret Word from the Word List . 96
Displaying the Board to the Player . 97
The list() and range() Functions . 98
List and String Slicing . 98
Displaying the Secret Word with Blanks 99
Getting the Player’s Guess 101
The lower() and upper() String Methods 101
Leaving the while Loop . 103
elif Statements 103
Making Sure the Player Entered a Valid Guess . 104
Asking the Player to Play Again 104
Review of the Hangman Functions . 105
The Game Loop 105
Calling the displayBoard() Function 106
Letting the Player Enter Their Guess 106
Checking Whether the Letter Is in the Secret Word . 106
Checking Whether the Player Won 107
Handling an Incorrect Guess . 107
Checking Whether the Player Lost 108
Ending or Resetting the Game 108
Summary . 109
9 Extending Hangman 111
Adding More Guesses . 112
The Dictionary Data Type . 112
Getting the Size of Dictionaries with len() 113
The Difference Between Dictionaries and Lists 113
The keys() and values() Dictionary Methods . 114
Using Dictionaries of Words in Hangman . 115
Randomly Choosing from a List . 115
Deleting Items from Lists . 117
Multiple Assignment 118
Printing the Word Category for the Player 119
Summary . 120
10 Tic-Ta c-Toe 121
Sample Run of Tic-Tac-Toe 122
Source Code for Tic-Tac-Toe . 123
Designing the Program 127
Representing the Board as Data . 127
Strategizing with the Game AI . 128
Importing the random Module 129
Printing the Board on the Screen . 129
Letting the Player Choose X or O . 130
Deciding Who Goes First . 131
Placing a Mark on the Board 131
List References . 132
Using List References in makeMove() 135
Checking Whether the Player Won . 135
Duplicating the Board Data 137
Checking Whether a Space on the Board Is Free 138
Letting the Player Enter a Move . 138
Contents in Detail xiii
Short-Circuit Evaluation 139
Choosing a Move from a List of Moves 141
The None Value 142
Creating the Computer’s AI 142
Checking Whether the Computer Can Win in One Move . 143
Checking Whether the Player Can Win in One Move . 144
Checking the Corner, Center, and Side Spaces (in That Order) . 144
Checking Whether the Board Is Full 145
The Game Loop 145
Choosing the Player’s Mark and Who Goes First . 146
Running the Player’s Turn 146
Running the Computer’s Turn . 147
Asking the Player to Play Again . 148
Summary . 148
11 The Bagels Deduction Game 149
Sample Run of Bagels 150
Source Code for Bagels . 151
Flowchart for Bagels 152
Importing random and Defining getSecretNum() . 153
Shuffling a Unique Set of Digits . 154
Changing List Item Order with the random.shuffle() Function 154
Getting the Secret Number from the Shuffled Digits 154
Augmented Assignment Operators 155
Calculating the Clues to Give . 156
The sort() List Method . 157
The join() String Method . 158
Checking Whether a String Has Only Numbers 158
Starting the Game . 159
String Interpolation 159
The Game Loop 160
Getting the Player’s Guess . 161
Getting the Clues for the Player’s Guess 161
Checking Whether the Player Won or Lost 161
Asking the Player to Play Again . 162
Summary . 162
12 The Cartesian Coordinate System 163
Grids and Cartesian Coordinates 164
Negative Numbers 166
The Coordinate System of a Computer Screen 167
Math Tricks 168
Trick 1: A Minus Eats the Plus Sign on Its Left . 168
Trick 2: Two Minuses Combine into a Plus . 169
Trick 3: Two Numbers Being Added Can Swap Places . 169
Absolute Values and the abs() Function 170
Summary . 170
13 Sonar Treasure Hunt 171
Sample Run of Sonar Treasure Hunt  173
Source Code for Sonar Treasure Hunt 175
Designing the Program 180
Importing the random, sys, and math Modules 180
Creating a New Game Board 180
Drawing the Game Board 181
Drawing the X-Coordinates Along the Top of the Board 182
Drawing the Ocean 183
Printing a Row in the Ocean 184
Drawing the X-Coordinates Along the Bottom of the Board 184
Creating the Random Treasure Chests 184
Determining Whether a Move Is Valid . 185
Placing a Move on the Board . 185
Finding the Closest Treasure Chest . 186
Removing Values with the remove() List Method . 189
Getting the Player’s Move . 190
Printing the Game Instructions for the Player . 191
The Game Loop 192
Displaying the Game Status for the Player . 193
Handling the Player’s Move . 193
Finding a Sunken Treasure Chest . 194
Checking Whether the Player Won 194
Checking Whether the Player Lost 195
Terminating the Program with the sys.exit() Function . 195
Summary . 196
14 Caesar Cipher 197
Cryptography and Encryption . 198
How the Caesar Cipher Works . 199
Sample Run of Caesar Cipher 200
Source Code for Caesar Cipher 201
Setting the Maximum Key Length . 202
Deciding to Encrypt or Decrypt the Message 202
Getting the Message from the Player . 203
Getting the Key from the Player . 203
Encrypting or Decrypting the Message . 203
Finding Passed Strings with the find() String Method . 204
Encrypting or Decrypting Each Letter 205
Starting the Program 206
The Brute-Force Technique 206
Adding the Brute-Force Mode . 207
Summary . 208
15 The Reversegam Game 209
How to Play Reversegam 210
Sample Run of Reversegam 213
Contents in Detail xv
Source Code for Reversegam . 215
Importing Modules and Setting Up Constants 220
The Game Board Data Structure 220
Drawing the Board Data Structure on the Screen 221
Creating a Fresh Board Data Structure 222
Checking Whether a Move Is Valid . 222
Checking Each of the Eight Directions . 223
Finding Out Whether There Are Tiles to Flip Over 224
Checking for Valid Coordinates 225
Getting a List with All Valid Moves . 226
Calling the bool() Function 227
Getting the Score of the Game Board 227
Getting the Player’s Tile Choice 228
Determining Who Goes First 228
Placing a Tile on the Board 229
Copying the Board Data Structure . 229
Determining Whether a Space Is on a Corner 230
Getting the Player’s Move 230
Getting the Computer’s Move . 232
Strategizing with Corner Moves . 232
Getting a List of the Highest-Scoring Moves . 233
Printing the Scores to the Screen . 234
Starting the Game . 234
Checking for a Stalemate 234
Running the Player’s Turn 235
Running the Computer’s Turn . 236
The Game Loop 237
Asking the Player to Play Again 238
Summary . 238
16 Reversegam AI Simulation 239
Making the Computer Play Against Itself 240
Sample Run of Simulation 1 . 240
Source Code for Simulation 1 241
Removing the Player Prompts and Adding a Computer Player 242
Making the Computer Play Itself Several Times 243
Sample Run of Simulation 2 . 243
Source Code for Simulation 2 244
Keeping Track of Multiple Games 245
Commenting Out print() Function Calls 245
Using Percentages to Grade the AIs . 246
Comparing Different AI Algorithms 247
Source Code for Simulation 3 248
How the AIs Work in Simulation 3 . 249
Comparing the AIs . 252
Summary . 254
17 Creating Graphics 255
Installing pygame 256
Hello World in pygame . 256
Sample Run of pygame Hello World . 257
Source Code for pygame Hello World . 257
Importing the pygame Module 259
Initializing pygame 259
Setting Up the pygame Window . 260
Tuples . 260
Surface Objects . 261
Setting Up Color Variables . 261
Writing Text on the pygame Window 262
Using Fonts to Style Text 262
Rendering a Font Object . 263
Setting the Text Location with Rect Attributes 264
Filling a Surface Object with a Color . 266
pygame’s Drawing Functions 266
Drawing a Polygon 266
Drawing a Line 267
Drawing a Circle . 268
Drawing an Ellipse . 268
Drawing a Rectangle 268
Coloring Pixels 269
The blit() Method for Surface Objects  270
Drawing the Surface Object to the Screen 270
Events and the Game Loop . 270
Getting Event Objects . 271
Exiting the Program 271
Summary . 272
18 Animating Graphics 273
Sample Run of the Animation Program . 274
Source Code for the Animation Program 274
Moving and Bouncing the Boxes . 276
Setting Up the Constant Variables . 277
Constant Variables for Direction . 277
Constant Variables for Color . 278
Setting Up the Box Data Structures 278
The Game Loop 279
Handling When the Player Quits 279
Moving Each Box . 280
Bouncing a Box . 281
Drawing the Boxes on the Window in Their New Positions 282
Drawing the Window on the Screen . 282
Summary . 283
19 Collision Detection 285
Sample Run of the Collision Detection Program . 286
Source Code for the Collision Detection Program 287
Importing the Modules . 289
Using a Clock to Pace the Program . 289
Setting Up the Window and Data Structures . 290
Setting Up Variables to Track Movement 291
Handling Events 292
Handling the KEYDOWN Event . 293
Handling the KEYUP Event 294
Teleporting the Player 295
Adding New Food Squares 295
Moving the Player Around the Window . 296
Drawing the Player on the Window 297
Checking for Collisions . 297
Drawing the Food Squares on the Window 298
Summary . 299
20 Using Sounds and Images 301
Adding Images with Sprites 302
Sound and Image Files 302
Sample Run of the Sprites and Sounds Program 303
Source Code for the Sprites and Sounds Program . 304
Setting Up the Window and the Data Structure . 306
Adding a Sprite . 307
Changing the Size of a Sprite 307
Setting Up the Music and Sounds 307
Adding Sound Files 308
Toggling the Sound On and Off . 308
Drawing the Player on the Window . 309
Checking for Collisions 309
Drawing the Cherries on the Window 310
Summary . 310
21 A Dodger Game with Sounds and Images 311
Review of the Basic pygame Data Types 312
Sample Run of Dodger . 313
Source Code for Dodger 313
Importing the Modules . 317
Setting Up the Constant Variables . 318
Defining Functions . 319
Ending and Pausing the Game  319
Keeping Track of Baddie Collisions 320
Drawing Text to the Window . 320
xviii Contents in Detail
Initializing pygame and Setting Up the Window . 321
Setting Up Font, Sound, and Image Objects . 322
Displaying the Start Screen . 323
Starting the Game 324
The Game Loop 325
Handling Keyboard Events 325
Handling Mouse Movement . 327
Adding New Baddies 327
Moving the Player’s Character and the Baddies 328
Implementing the Cheat Codes . 329
Removing the Baddies . 330
Drawing the Window 330
Drawing the Player’s Score . 331
Drawing the Player’s Character and Baddies . 331
Checking for Collisions 332
The Game Over Screen . 332
Modifying the Dodger Game 333
Summary . 334
Index 335


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Who Is This Book For?
Programming isn’t hard, but it is hard to find materials that teach you to
do interesting things with programming. Other computer books go over
many topics most new coders don’t need. This book will teach you how to
program your own games; you’ll learn a useful skill and have fun games to
show for it! This book is for:
• Complete beginners who want to teach themselves programming, even
if they have no previous experience.
• Kids and teenagers who want to learn programming by creating games.
• Adults and teachers who wish to teach others programming.
• Anyone, young or old, who wants to learn how to program by learning a
professional programming language.

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