Learn Python 3 the Hard Way

Zed A. Shaw is the author of the popular online books Learn Python the Hard Way, Learn Ruby the Hard Way, and Learn C the Hard Way. He is also the creator of several open source software projects and has been programming and writing for nearly 20 years. Most of his free time is devoted to the study of painting and art history.

Preface xvii

Acknowledgments xx

Exercise 0: The Setup 2

macOS 2

Windows 3

Linux 4

Finding Things on the Internet 5

Warnings for Beginners 6

Alternative Text Editors 6

Exercise 1: A Good First Program 8

What You Should See 10

Study Drills 12

Common Student Questions 12

Exercise 2: Comments and Pound Characters 14

What You Should See 14

Study Drills 14

Common Student Questions 15

Exercise 3: Numbers and Math 16

What You Should See 17

Study Drills 17

Common Student Questions 17

Exercise 4: Variables and Names 20

What You Should See 21

Study Drills 21

Common Student Questions 21

Exercise 5: More Variables and Printing 24

What You Should See 24

Study Drills 25

Common Student Questions 25

Exercise 6: Strings and Text 26

What You Should See 27

Study Drills 27

Break It 27

Common Student Questions 27

Exercise 7: More Printing 28

What You Should See 28

Study Drills 29

Break It 29

Common Student Questions 29

Exercise 8: Printing, Printing 30

What You Should See 30

Study Drills 31

Common Student Questions 31

Exercise 9: Printing, Printing, Printing 32

What You Should See 32

Study Drills 33

Common Student Questions 33

Exercise 10: What Was That? 34

What You Should See 35

Escape Sequences 35

Study Drills 36

Common Student Questions 36

Exercise 11: Asking Questions 38

What You Should See 38

Study Drills 39

Common Student Questions 39

Exercise 12: Prompting People 40

What You Should See 40

Study Drills 40

Common Student Questions 41

Exercise 13: Parameters, Unpacking, Variables 42

Hold Up! Features Have Another Name 42

What You Should See 43

Study Drills 44

Common Student Questions 44

Exercise 14: Prompting and Passing 46

What You Should See 46

Study Drills 47

Common Student Questions 47

Exercise 15: Reading Files 48

What You Should See 49

Study Drills 49

Common Student Questions 50

Exercise 16: Reading and Writing Files 52

What You Should See 53

Study Drills 53

Common Student Questions 54

Exercise 17: More Files 56

What You Should See 56

Study Drills 57

Common Student Questions 57

Exercise 18: Names, Variables, Code, Functions 60

What You Should See 61

Study Drills 62

Common Student Questions 62

Exercise 19: Functions and Variables 64

What You Should See 65

Study Drills 65

Common Student Questions 65

Exercise 20: Functions and Files 68

What You Should See 69

Study Drills 69

Common Student Questions 69

Exercise 21: Functions Can Return Something 72

What You Should See 73

Study Drills 73

Common Student Questions 74

Exercise 22: What Do You Know So Far? 76

What You Are Learning 76

Exercise 23: Strings, Bytes, and Character Encodings 78

Initial Research 78

Switches, Conventions, and Encodings 80

Disecting the Output 82

Disecting the Code 82

Encodings Deep Dive 84

Breaking It 85

Exercise 24: More Practice 86

What You Should See 87

Study Drills 87

Common Student Questions 87

Exercise 25: Even More Practice 90

What You Should See 91

Study Drills 92

Common Student Questions 93

Exercise 26: Congratulations, Take a Test! 94

Common Student Questions 94

Exercise 27: Memorizing Logic 96

The Truth Terms 96

The Truth Tables 97

Common Student Questions 98

Exercise 28: Boolean Practice 100

What You Should See 102

Study Drills 102

Common Student Questions 102

Exercise 29: What If 104

What You Should See 104

Study Drills 105

Common Student Questions 105

Exercise 30: Else and If 106

What You Should See 107

Study Drills 107

Common Student Questions 107

Exercise 31: Making Decisions 108

What You Should See 109

Study Drills 109

Common Student Questions 109

Exercise 32: Loops and Lists 112

What You Should See 113

Study Drills 114

Common Student Questions 114

Exercise 33: While Loops 116

What You Should See 117

Study Drills 117

Common Student Questions 118

Exercise 34: Accessing Elements of Lists 120

Study Drills 121

Exercise 35: Branches and Functions 122

What You Should See 123

Study Drills 124

Common Student Questions 124

Exercise 36: Designing and Debugging 126

Rules for if-statements 126

Rules for Loops 126

Tips for Debugging 127

Homework 127

Exercise 37: Symbol Review 128

Keywords 128

Data Types 129

String Escape Sequences 130

Old Style String Formats 130

Operators 131

Reading Code 132

Study Drills 133

Common Student Questions 133

Exercise 38: Doing Things to Lists 134

What You Should See 135

What Lists Can Do 136

When to Use Lists 137

Study Drills 137

Common Student Questions 138

Exercise 39: Dictionaries, Oh Lovely Dictionaries 140

A Dictionary Example 141

What You Should See 142

What Dictionaries Can Do 143

Study Drills 144

Common Student Questions 144

Exercise 40: Modules, Classes, and Objects 146

Modules Are Like Dictionaries 146

What You Should See 150

Study Drills 150

Common Student Questions 151

Exercise 41: Learning to Speak Object-Oriented 152

Word Drills 152

Phrase Drills 152

Combined Drills 153

A Reading Test 153

Practice English to Code 155

Reading More Code 156

Common Student Questions 156

Exercise 42: Is-A, Has-A, Objects, and Classes 158

How This Looks in Code 159

About class Name(object) 161

Study Drills 161

Common Student Questions 161

Exercise 43: Basic Object-Oriented Analysis and Design 164

The Analysis of a Simple Game Engine 165

Top Down versus Bottom Up 169

The Code for “Gothons from Planet Percal #25” 170

What You Should See 176

Study Drills 176

Common Student Questions 177

Exercise 44: Inheritance versus Composition 178

What Is Inheritance? 178

The Reason for super() 183

Composition 184

When to Use Inheritance or Composition 185

Study Drills 185

Common Student Questions 186

Exercise 45: You Make a Game 188

Evaluating Your Game 188

Function Style 189

Class Style 189

Code Style 190

Good Comments 190

Evaluate Your Game 190

Exercise 46: A Project Skeleton 192

macOS/Linux Setup 192

Windows 10 Setup 194

Creating the Skeleton Project Directory 195

Testing Your Setup 197

Using the Skeleton 198

Required Quiz 198

Common Student Questions 198

Exercise 47: Automated Testing 200

Writing a Test Case 200

Testing Guidelines 202

What You Should See 202

Study Drills 203

Common Student Questions 203

Exercise 48: Advanced User Input 204

Our Game Lexicon 204

A Test First Challenge 206

What You Should Test 207

Study Drills 209

Common Student Questions 209

Exercise 49: Making Sentences 210

Match and Peek 210

The Sentence Grammar 211

A Word on Exceptions 211

The Parser Code 211

Playing with the Parser 214

What You Should Test 215

Study Drills 215

Common Student Questions 215

Exercise 50: Your First Website 216

Installing flask 216

Make a Simple “Hello World” Project 216

What’s Going On? 218

Fixing Errors 218

Create Basic Templates 219

Study Drills 221

Common Student Questions 221

Exercise 51: Getting Input from a Browser 224

How the Web Works 224

How Forms Work 226

Creating HTML Forms 227

Creating a Layout Template 229

Writing Automated Tests for Forms 230

Study Drills 232

Breaking It 232

Exercise 52: The Start of Your Web Game 234

Refactoring the Exercise 43 Game 234

Creating an Engine 239

Your Final Exam 241

Common Student Questions 242

Next Steps 244

How to Learn Any Programming Language 245

Advice from an Old Programmer 246

Appendix Command Line Crash Course 248

Introduction: Shut Up and Shell 248

The Setup 249

Paths, Folders, Directories (pwd) 253

If You Get Lost 255

Make a Directory (mkdir) 255

Change Directory (cd) 258

List Directory (ls) 261

Remove Directory (rmdir) 265

Moving Around (pushd, popd) 268

Making Empty Files (touch/New-Item) 271

Copy a File (cp) 272

Moving a File (mv) 275

View a File (less/more) 277

Stream a File (cat) 278

Removing a File (rm) 280

Exiting Your Terminal (exit) 282

Command Line Next Steps 283

Index 284