Python Programming with Design Patterns

Improve Your Python Code with Modern Object-Oriented Design Patterns To write clean, efficient, maintainable code, developers everywhere turn to design patterns. Now there's a Python-specific patterns guide that's friendly and practical enough for every Python developer, regardless of experience. Best-selling patterns author James W. Cooper presents visual, example-driven explanations of 23 proven patterns for writing superior object-oriented code. Through clear and intuitive code samples, he introduces modern techniques for creating Python objects that interact effectively in powerful, flexible programs. Python newcomers--including those moving from other languages--will find a succinct introduction designed to get them up to speed fast. Cooper's wide-ranging patterns coverage addresses abstract classes, multiple inheritance, GUI programming and widgets, graphical classes, drawing and plotting, math, databases, Python decorators, images, threads, iterators, creating executable code, and more. Throughout, his informal visual presentation makes patterns far easier to work with--so you can confidently build sophisticated programs that use Python's rich capabilities. Review the essentials of Python objects and visual programming Learn what design patterns are, and how they help you write better code Use creational patterns to enhance flexibility and avoid unnecessary complexity Apply structural patterns to ensure that program elements work together well in large programs Optimize communication between objects with behavioral patterns

Table of Contents:
Preface xxi PART I: INTRODUCTION 1 The tkinter Library 2 GitHub 2 Chapter 1 Introduction to Objects 5 The Class __init__ Method 6 Variables Inside a Class 6 Collections of Classes 7 Inheritance 8 Derived Classes Created with Revised Methods 8 Multiple Inheritance 8 Drawing a Rectangle and a Square 10 Visibility of Variables 12 Properties 13 Local Variables 13 Types in Python 13 Summary 14 Programs on GitHub 15 Chapter 2 Visual Programming in Python 17 Importing Fewer Names 19 Creating an Object-Oriented Version 19 Using Message Boxes 21 Using File Dialogs 22 Understanding Options for the Pack Layout Manager 23 Using the ttk Libraries 24 Responding to User Input 25 Adding Two Numbers 26 Catching the Error 26 Applying Colors in tkinter 27 Creating Radio Buttons 27 Using a Class-Level Variable 30 Communicating Between Classes 30 Using the Grid Layout 30 Creating Checkbuttons 32 Disabling Check Boxes 32 Adding Menus to Windows 35 Using the LabelFrame 39 Moving On 40 Examples on GitHub 40 Chapter 3 Visual Programming of Tables of Data 41 Creating a Listbox 42 Displaying the State Data 44 Using a Combobox 46 The Treeview Widget 47 Inserting Tree Nodes 50 Moving On 51 Example Code on GitHub 51 Chapter 4 What Are Design Patterns? 53 Defining Design Patterns 54 The Learning Process 55 Notes on Object-Oriented Approaches 56 Python Design Patterns 57 References 57 PART II: CREATIONAL PATTERNS 59 Chapter 5 The Factory Pattern 61 How a Factory Works 61 Sample Code 62 The Two Subclasses 62 Building the Simple Factory 63 Using the Factory 63 A Simple GUI 64 Factory Patterns in Math Computation 65 Programs on GitHub 65 Thought Questions 66 Chapter 6 The Factory Method Pattern 67 The Swimmer Class 68 The Event Classes 69 Straight Seeding 70 Circle Seeding 71 Our Seeding Program 72 Other Factories 74 When to Use a Factory Method 74 Programs on GitHub 74 Chapter 7 The Abstract Factory Pattern 75 A GardenMaker Factory 75 How the User Interface Works 77 Consequences of the Abstract Factory Pattern 77 Thought Questions 78 Code on GitHub 78 Chapter 8 The Singleton Pattern 79 Throwing the Exception 80 Creating an Instance of the Class 80 Static Classes As Singleton Patterns 81 Finding the Singletons in a Large Program 81 Other Consequences of the Singleton Pattern 82 Sample Code on GitHub 82 Chapter 9 The Builder Pattern 83 An Investment Tracker 84 Calling the Builders 86 The List Box Builder 87 The Checkbox Builder 88 Displaying the Selected Securities 89 Consequences of the Builder Pattern 89 Thought Questions 89 Sample Code on GitHub 89 Chapter 10 The Prototype Pattern 91 Cloning in Python 91 Using the Prototype 92 Consequences of the Prototype Pattern 94 Sample Code on GitHub 94 Chapter 11 Summary of Creational Patterns 95 PART III: STRUCTURAL PATTERNS 97 Chapter 12 The Adapter Pattern 99 Moving Data Between Lists 99 Making an Adapter 101 The Class Adapter 103 Two-Way Adapters 103 Pluggable Adapters 103 Programs on GitHub 103 Chapter 13 The Bridge Pattern 105 Creating the User Interface 107 Extending the Bridge 108 Consequences of the Bridge Pattern 109 Programs on GitHub 110 Chapter 14 The Composite Pattern 111 An Implementation of a Composite 112 Salary Computation 112 The Employee Classes 112 The Boss Class 113 Building the Employee Tree 114 Printing the Employee Tree 114 Creating a Treeview of the Composite 116 Using Doubly Linked Lists 117 Consequences of the Composite Pattern 118 A Simple Composite 119 Other Implementation Issues 119 Dealing with Recursive Calls 119 Ordering Components 120 Caching Results 120 Programs on GitHub 120 Chapter 15 The Decorator Pattern 121 Decorating a Button 121 Using a Decorator 122 Using Nonvisual Decorators 123 Decorated Code 124 The dataclass Decorator 125 Using dataclass with Default Values 126 Decorators, Adapters, and Composites 126 Consequences of the Decorator Pattern 126 Programs on GitHub 127 Chapter 16 The Facade Pattern 129 Building the Façade Classes 131 Creating Databases and Tables 135 Using the SQLite Version 136 Consequences of the Façade 137 Programs on GitHub 137 Notes on MySQL 137 Using SQLite 138 References 138 Chapter 17 The Flyweight Pattern 139 What Are Flyweights? 139 Example Code 140 Selecting a Folder 142 Copy-on-Write Objects 143 Program on GitHub 143 Chapter 18 The Proxy Pattern 145 Using the Pillow Image Library 145 Displaying an Image Using PIL 146 Using Threads to Handle Image Loading 146 Logging from Threads 149 Copy-on-Write 149 Comparing Related Patterns 149 Programs on GitHub 150 Chapter 19 Summary of Structural Patterns 151 PART IV: BEHAVIORAL PATTERNS 153 Chapter 20 Chain of Responsibility Pattern 155 When to Use the Chain 156 Sample Code 156 The Listboxes 159 Programming a Help System 160 Receiving the Help Command 161 The First Case 162 A Chain or a Tree? 163 Kinds of Requests 164 Consequences of the Chain of Responsibility 164 Programs on GitHub 165 Chapter 21 The Command Pattern 167 When to Use the Command Pattern 167 Command Objects 168 A Keyboard Example 168 Calling the Command Objects 170 Building Command Objects 171 The Command Pattern 172 Consequences of the Command Pattern 172 Providing the Undo Function 172 Creating the Red and Blue Buttons 175 Undoing the Lines 175 Summary 176 References 176 Programs on GitHub 176 Chapter 22 The Interpreter Pattern 177 When to Use an Interpreter 177 Where the Pattern Can Be Helpful 177 A Simple Report Example 178 Interpreting the Language 179 How Parsing Works 180 Sorting Using attrgetter() 181 The Print Verb 182 The Console Interface 182 The User Interface 183 Consequences of the Interpreter Pattern 184 Programs on GitHub 185 Chapter 23 The Iterator Pattern 187 Why We Use Iterators 187 Iterators in Python 187 A Fibonacci Iterator 188 Getting the Iterator 189 Filtered Iterators 189 The Iterator Generator 191 A Fibonacci Iterator 191 Generators in Classes 192 Consequences of the Iterator Pattern 192 Programs on GitHub 193 Chapter 24 The Mediator Pattern 195 An Example System 195 Interactions Between Controls 197 Sample Code 198 Mediators and Command Objects 199 Consequences of the Mediator Pattern 200 Single Interface Mediators 200 Programs on GitHub 201 Chapter 25 The Memento Pattern 203 When to Use a Memento 203 Sample Code 204 Consequences of the Memento Pattern 209 Programs on GitHub 209 Chapter 26 The Observer Pattern 211 Example Program for Watching Colors Change 212 The Message to the Media 215 Consequences of the Observer Pattern 215 Programs on GitHub 215 Chapter 27 The State Pattern 217 Sample Code 217 Switching Between States 221 How the Mediator Interacts with the State State Transitions 224 Programs on GitHub 224 Chapter 28 The Strategy Pattern 225 Why We Use the Strategy Pattern 225 Sample Code 226 The Context 227 The Program Commands 227 The Line and Bar Graph Strategies 228 Consequences of the Strategy Pattern 230 Programs on GitHub 231 Chapter 29 The Template Pattern 233 Why We Use Template Patterns 233 Kinds of Methods in a Template Class 234 Sample Code 234 Drawing a Standard Triangle 235 Drawing an Isosceles Triangle 236 The Triangle Drawing Program 237 Templates and Callbacks 238 Summary and Consequences 238 Example Code on GitHub 238 Chapter 30 The Visitor Pattern 239 When to Use the Visitor Pattern 239 Working with the Visitor Pattern 241 Sample Code 241 Visiting Each Class 242 Visiting Several Classes 242 Bosses Are Employees, Too 243 Double Dispatching 245 Traversing a Series of Classes 245 Consequences of the Visitor Pattern 245 Example Code on GitHub 245 PART V: A BRIEF INTRODUCTION TO PYTHON 247 Chapter 31 Variables and Syntax in Python 249 Data Types 250 Numeric Constants 250 Strings 250 Character Constants 251 Variables 252 Complex Numbers 253 Integer Division 253 Multiple Equal Signs for Initialization 254 A Simple Python Program 254 Compiling and Running This Program 255 Arithmetic Operators 255 Bitwise Operators 255 Combined Arithmetic and Assignment Statements 256 Comparison Operators 256 The input Statement 257 PEP 8 Standards 258 Variable and Function Names 258 Constants 258 Class Names 258 Indentation and Spacing 259 Comments 259 Docstrings 259 String Methods 260 Examples on GitHub 261 Chapter 32 Making Decisions in Python 263 elif is “else if” 263 Combining Conditions 264 The Most Common Mistake 264 Looping Statements in Python 265 The for Loop and Lists 265 Using range in if Statements 266 Using break and continue 266 The continue Statement 267 Python Line Length 267 The print Function 267 Formatting Numbers 268 C and Java Style Formatting 269 The format string Function 269 f-string Formatting 269 Comma-Separated Numbers 270 Strings 270 Formatting Dates 271 Using the Python match Function 271 Pattern Matching 272 Reference 273 Moving On 273 Sample Code on GitHub 273 Chapter 33 Development Environments 275 IDLE 275 Thonny 275 PyCharm 276 Visual Studio 276 Other Development Environments 276 LiClipse 276 Jupyter Notebook 277 Google Colaboratory 277 Anaconda 277 Wing 278 Command-Line Execution 278 CPython, IPython, and Jython 278 Chapter 34 Python Collections and Files 279 Slicing 279 Slicing Strings 280 Negative Indexes 281 String Prefix and Suffix Removal 281 Changing List Contents 281 Copying a List 282 Reading Files 282 Using the with Loop 283 Handling Exceptions 284 Using Dictionaries 284 Combining Dictionaries 286 Using Tuples 286 Using Sets 287 Using the map Function 287 Writing a Complete Program 288 Impenetrable Coding 288 Using List Comprehension 289 Sample Programs on GitHub 290 Chapter 35 Functions 291 Returning a Tuple 292 Where Does the Program Start? 292 Summary 293 Programs on GitHub 293 Appendix A Running Python Programs 295 If You Have Python Installed 295 Shortcuts 295 Creating an Executable Python Program 296 Command-Line Arguments 297 Index 299

About the Author :
James W. Cooper holds a PhD in chemistry and worked in academia, for the scientific instrument industry, and for IBM for 25 years, primarily as a computer scientist at IBM's Thomas J. Watson Research Center. Now retired, he is the author of 20 books, including 3 on design patterns in various languages. His most recent books are Flameout: The Rise and Fall of IBM Instruments (2019) and Food Myths Debunked (2014). James holds 11 patents and has written 60 columns for JavaPro Magazine. He has also written nearly 1,000 columns for the now vanished Examiner.com on foods and chemistry, and he currently writes his own blog: FoodScienceInstitute.com. Recently, he has written columns on Python for Medium.com and Substack. He is also involved in local theater groups and is the treasurer for Troupers Light Opera, where he performs regularly.