SOLID principles, introduced by Robert C. Martin, aim to make software design more flexible, maintainable, and scalable. The principles include Single Responsibility (S), Open/Closed (O), Liskov Substitution (L), Interface Segregation (I), and Dependency Inversion (D). Each principle is detailed with core ideas, explanations, code examples, and benefits. Following these principles leads to clearer, more concise code that is easier to test, maintain, and reuse. The principles enhance extensibility, reduce risks of code modifications, maintain inheritance consistency, improve code reliability, increase system stability, ensure correct polymorphism implementation, enhance flexibility, and reduce system coupling.

本文介绍了三个常见的设计模式在Python中的应用。首先是**单例模式**，通过实现一个数据库连接池管理器来确保系统中只有一个连接池实例。其次是**工厂模式**，设计一个文件处理系统，支持多种数据格式的解析，并通过工厂类创建对应的解析器。最后是**观察者模式**，实现一个股票市场监控系统，当股票价格变化时通知注册的观察者，包括邮件通知、短信通知和应用内通知等。这些设计模式在实际开发中能够提高系统的灵活性和可维护性。