SOLID principles, including Single Responsibility Principle (S), Open/Closed Principle (O), Liskov Substitution Principle (L), Interface Segregation Principle (I), and Dependency Inversion Principle (D), aim to improve software design by promoting flexibility, maintainability, and extensibility. Each principle is detailed with examples and benefits. For example, adherence to Single Responsibility Principle leads to clearer, more concise code with reduced coupling between classes. Similarly, following Open/Closed Principle enhances code scalability and stability by favoring extension over modification. Liskov Substitution Principle ensures consistency and reliability in inheritance hierarchies, while Interface Segregation Principle increases code flexibility and reusability by avoiding unnecessary method implementations. Lastly, Dependency Inversion Principle emphasizes abstract dependencies over concrete ones, promoting decoupling and control inversion for better code maintenance and scalability.

本文介绍了三种常见设计模式的Python实现。首先是单例模式，实现了一个数据库连接池管理器，确保系统中只有一个连接池实例，具有最大连接数限制。其次是工厂模式，设计了一个支持多种数据格式解析的文件处理系统，通过工厂方法创建对应的解析器处理CSV、JSON、XML和YAML文件。最后是观察者模式，实现了一个股票市场监控系统，支持多种观察者（邮件、短信、应用内通知），在股票价格变化时通知观察者。这三种设计模式为软件架构设计提供了灵活性和可扩展性。