Mastering Python Design Patterns: Craft essential Python patterns by following core design principles. 3 Ed

Cover....1

Title Page....2

Copyright....3

Dedication....4

Contributors....5

Table of Contents....8

Preface....14

Part 1: Start with Principles....20

Chapter 1: Foundational Design Principles....22

Technical requirements....23

Following the Encapsulate What Varies principle....23

What does it mean?....23

Benefits....23

Techniques for achieving encapsulation....24

An example – encapsulating using polymorphism....25

An example – encapsulating using a property....26

Following the Favor Composition Over Inheritance principle....28

What does it mean?....28

Benefits....29

Techniques for composition....29

An example – compose a car using the engine....29

Following the Program to Interfaces, Not Implementations principle....31

What does it mean?....31

Benefits....31

Techniques for interfaces....31

An example – different types of logger....33

An example – different types of logger, now using Protocols....35

Following the Loose Coupling principle....37

What does it mean?....37

Benefits....37

Techniques for loose coupling....37

An example – a message service....38

Summary....40

Chapter 2: SOLID Principles....42

Technical requirements....42

SRP....42

An example of software design following the SRP....43

OCP....45

An example of design following the OCP....46

LSP....49

An example of design following the LSP....49

ISP....52

An example of design following the ISP....52

DIP....55

An example of design following the ISP....56

Summary....58

Part 2: From the Gang of Four....60

Chapter 3: Creational Design Patterns....62

Technical requirements....63

The factory pattern....63

The factory method....63

The abstract factory pattern....72

The builder pattern....77

Real-world examples....78

Comparison with the factory pattern....78

Use cases for the builder pattern....78

Implementing the builder pattern....78

The prototype pattern....83

Real-world examples....83

Use cases for the prototype pattern....84

Implementing the prototype pattern....84

The singleton pattern....88

Real-world examples....88

Use cases for the singleton pattern....89

Implementing the singleton pattern....89

Should you use the singleton pattern?....92

The object pool pattern....92

Real-world examples....92

Use cases for the object pool pattern....93

Implementing the object pool pattern....93

Summary....95

Chapter 4: Structural Design Patterns....96

The adapter pattern....96

Real-world examples....97

Use cases for the adapter pattern....97

Implementing the adapter pattern – adapt a legacy class....97

Implementing the adapter pattern – adapt several classes into a unified interface....99

The decorator pattern....102

Real-world examples....103

Use cases for the decorator pattern....103

Implementing the decorator pattern....104

The bridge pattern....108

Real-world examples....109

Use cases for the bridge pattern....109

Implementing the bridge pattern....109

The facade pattern....112

Real-world examples....112

Use cases for the facade pattern....113

Implementing the facade pattern....113

The flyweight pattern....117

Real-world examples....117

Use cases for the flyweight pattern....118

Implementing the flyweight pattern....118

The proxy pattern....122

Real-world examples....122

Use cases for the proxy pattern....123

Implementing the proxy pattern – a virtual proxy....123

Implementing the proxy pattern – a protection proxy....126

Implementing the proxy pattern – a remote proxy....128

Implementing the proxy pattern – a smart proxy....130

Summary....133

Chapter 5: Behavioral Design Patterns....136

Technical requirements....137

The Chain of Responsibility pattern....137

Real-world examples....137

Use cases for the Chain of Responsibility pattern....138

Implementing the Chain of Responsibility pattern....138

The Command pattern....142

Real-world examples....142

Use cases for the Command pattern....143

Implementing the Command pattern....143

The Observer pattern....147

Real-world examples....147

Use cases for the Observer pattern....148

Implementing the Observer pattern....148

The State pattern....151

Real-world examples....152

Use cases for the State pattern....153

Implementing the State pattern....153

The Interpreter pattern....159

Real-world examples....159

Use cases for the Interpreter pattern....159

Implementing the Interpreter pattern....160

The Strategy pattern....163

Real-world examples....164

Use cases for the Strategy pattern....164

Implementing the Strategy pattern....164

The Memento pattern....168

Real-world examples....168

Use cases for the Memento pattern....169

Implementing the Memento pattern....169

The Iterator pattern....172

Use cases for the Iterator pattern....172

Implementing the Iterator pattern....173

The Template pattern....175

Real-world examples....175

Use cases for the Template pattern....175

Implementing the Template pattern....176

Other behavioral design patterns....178

Summary....178

Part 3: Beyond the Gang of Four....180

Chapter 6: Architectural Design Patterns....182

Technical requirements....182

The MVC pattern....183

Real-world examples....184

Use cases for the MVC pattern....185

Implementing the MVC pattern....186

The Microservices pattern....188

Real-world examples....189

Use cases for the Microservices pattern....190

Implementing the microservices pattern – a payment service using gRPC....190

Implementing the microservices pattern – an LLM service using Lanarky....193

The Serverless pattern....196

Real-world examples....196

Use cases for the Serverless pattern....197

Implementing the Serverless pattern....197

The Event Sourcing pattern....199

Real-world examples....199

Use cases for the Event Sourcing pattern....199

Implementing the event sourcing pattern – the manual way....200

Implementing the Event Sourcing pattern – using a library....202

Other architectural design patterns....204

Summary....204

Chapter 7: Concurrency and Asynchronous Patterns....206

Technical requirements....206

The Thread Pool pattern....207

Real-world examples....207

Use cases for the Thread Pool pattern....208

Implementing the Thread Pool pattern....208

The Worker Model pattern....210

Real-world examples....210

Use cases for the Worker Model pattern....210

Implementing the Worker Model pattern....211

The Future and Promise pattern....213

Real-world examples....213

Use cases for the Future and Promise pattern....214

Implementing the Future and Promise pattern – using concurrent.futures....215

Implementing the Future and Promise pattern – using asyncio....216

The Observer pattern in reactive programming....218

Real-world examples....218

Use cases for the Observer pattern in reactive programming....219

Implementing the Observer pattern in reactive programming....219

Other concurrency and asynchronous patterns....222

Summary....223

Chapter 8: Performance Patterns....224

Technical requirements....224

The Cache-Aside pattern....225

Real-world examples....225

Use cases for the cache-aside pattern....225

Implementing the cache-aside pattern....225

The Memoization pattern....231

Real-world examples....232

Use cases for the memoization pattern....232

Implementing the memoization pattern....232

The Lazy Loading pattern....234

Real-world examples....234

Use cases for the lazy loading pattern....234

Implementing the lazy loading pattern – lazy attribute loading....235

Implementing the lazy loading pattern – using caching....236

Summary....238

Chapter 9: Distributed Systems Patterns....240

Technical requirements....240

The Throttling pattern....241

Real-world examples....241

Use cases for the Throttling pattern....242

Implementing the Throttling pattern....242

The Retry pattern....245

Real-world examples....245

Use cases for the Retry pattern....246

Implementing the Retry pattern....246

The Circuit Breaker pattern....248

Real-world examples....248

Use cases for the Circuit Breaker pattern....249

Implementing the Circuit Breaker pattern....249

Other distributed systems patterns....251

Summary....251

Chapter 10: Patterns for Testing....254

Technical requirements....254

The Mock Object pattern....254

Real-world examples....255

Use cases for the Mock Object pattern....255

Implementing the Mock Object pattern....256

The Dependency Injection pattern....258

Real-world examples....258

Use cases for the Dependency Injection pattern....258

Implementing the Dependency Injection pattern – using a mock object....259

Implementing the Dependency Injection pattern – using a decorator....261

Summary....265

Chapter 11: Python Anti-Patterns....266

Technical requirements....266

Code style violations....266

Tools for fixing coding style violations....267

Indentation....267

Maximum line length and blank lines....267

Imports....268

Naming conventions....268

Comments....269

Whitespace in expressions and statements....269

Correctness anti-patterns....270

Using the type() function for comparing types....270

Mutable default argument....271

Accessing a protected member from outside a class....273

Maintainability anti-patterns....274

Using a wildcard import....275

LBYL versus EAFP....275

Overusing inheritance and tight coupling....276

Using global variables for sharing data between functions....277

Performance anti-patterns....278

Not using .join() to concatenate strings in a loop....278

Using global variables for caching....279

Summary....281

Index....284

About Packt....292

Other Books You May Enjoy....293

As software systems become increasingly complex, maintaining code quality, scalability, and efficiency can be a daunting challenge. Mastering Python Design Patterns is an essential resource that equips you with the tools you need to overcome these hurdles and create robust, scalable applications.

The book delves into design principles and patterns in Python, covering both classic and modern patterns, and apply them to solve daily challenges as a Python developer or architect.

Co-authored by two Python experts with a combined experience of three decades, this new edition covers creational, structural, behavioral, and architectural patterns, including concurrency, asynchronous, and performance patterns. You'll find out how these patterns are relevant to various domains, such as event handling, concurrency, distributed systems, and testing. Whether you're working on user interfaces (UIs), web apps, APIs, data pipelines, or AI models, this book equips you with the knowledge to build robust and maintainable software. The book also presents Python anti-patterns, helping you avoid common pitfalls and ensuring your code remains clean and efficient.

 By the end of this book, you'll be able to confidently apply classic and modern Python design patterns to build robust, scalable applications.

What you will learn

• Master fundamental design principles and SOLID concepts
• Become familiar with Gang of Four (GoF) patterns and apply them effectively in Python
• Explore architectural design patterns to architect robust systems
• Delve into concurrency and performance patterns for optimized code
• Discover distributed systems patterns for scalable applications
• Get up to speed with testing patterns to ensure code reliability and maintainability
• Develop modular, decoupled systems and manage dependencies efficiently

Who this book is for

With a focus on intermediate and advanced Python programmers, this book offers valuable insights into the best practices for software design, backed by real-world examples and decades of experience. The book is also an excellent resource for software architects and team leaders who want to improve code quality and maintainability across their projects. Prior Python proficiency, including syntax, data structures, and OOP will help you get the most out of this book.