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