📚 Object-Oriented Programming in Python for Edexcel A-Level | 面向 Edexcel A-Level 的 Python 面向对象编程
Object-oriented programming (OOP) is a central paradigm in the Edexcel A-Level Computer Science specification. It allows you to model real-world entities using classes and objects, making code more modular, reusable, and easier to maintain. This article covers the key OOP concepts you need for Paper 2, with Python examples and exam-style explanations.
面向对象编程（OOP）是 Edexcel A-Level 计算机科学考试大纲中的核心范式。它允许你使用类和对象对现实世界中的实体进行建模，使代码更加模块化、可复用且易于维护。本文涵盖 Paper 2 所需的关键 OOP 概念，并提供 Python 示例和考试风格的解释。
1. Why OOP Matters in Edexcel A-Level | 为什么 OOP 在 Edexcel A-Level 中重要
Edexcel A-Level Computer Science expects you to understand how OOP supports abstraction, encapsulation, inheritance, and polymorphism. These four principles appear regularly in written questions and in the practical programming project. Mastering OOP helps you design solutions that are closer to real-world systems.
Edexcel A-Level 计算机科学要求你理解 OOP 如何支持抽象、封装、继承和多态。这四大原则经常出现在书面题和编程实践项目中。掌握 OOP 有助于你设计更接近现实系统的解决方案。
In the specification, OOP is linked to both theoretical understanding and practical coding. You may be asked to trace a class definition, identify errors in inheritance hierarchies, or write a short class from a scenario. Therefore, you need to be confident in reading and writing Python classes.
在考试大纲中，OOP 既与理论理解相关，也与实际编码相关。你可能需要追踪类定义、发现继承层次结构中的错误，或根据场景编写一个简短的类。因此，你需要自信地阅读和编写 Python 类。
- Abstraction hides unnecessary details and shows only essential features.
抽象隐藏不必要的细节，只显示基本特征。 - Encapsulation keeps data and methods together inside an object.
封装将数据和方法一起保存在对象内部。 - Inheritance allows a new class to reuse and extend an existing class.
继承允许新类复用并扩展现有类。 - Polymorphism lets the same method name behave differently in different classes.
多态允许相同的方法名在不同类中表现不同。
2. Classes and Objects: The Building Blocks | 类与对象：基本构建块
A class is a blueprint or template that defines the attributes and methods of a particular type of object. An object is a specific instance of a class, created at runtime. For example, the class Student describes what every student has, while the object student1 represents one particular student.
类是定义特定类型对象的属性和方法的蓝图或模板。对象是类在运行时创建的一个具体实例。例如，类 Student 描述了每个学生拥有什么，而对象 student1 代表一个特定的学生。
In Python, you create an object by calling the class name as if it were a function. Each object has its own copy of instance attributes, but methods are shared through the class definition. This distinction is important for understanding memory and behaviour in exam questions.
在 Python 中，你通过像调用函数一样调用类名来创建对象。每个对象都有自己的实例属性副本，但方法通过类定义共享。这种区别对于理解考试题中的内存和行为非常重要。
class Student:
pass
student1 = Student() # student1 is an object of the Student class
student2 = Student() # student2 is another independent object
The code above creates a minimal Student class with no attributes or methods. The two objects student1 and student2 are distinct instances, even though they come from the same blueprint.
上面的代码创建了一个最小的 Student 类，没有属性或方法。两个对象 student1 和 student2 是不同的实例，尽管它们来自同一个蓝图。
3. Defining a Class in Python | 在 Python 中定义类
A class definition begins with the keyword class, followed by the class name and a colon. By convention, class names use CamelCase, such as BankAccount or ExamResult. The body of the class contains methods, which are functions defined inside the class.
类定义以关键字 class 开头，后跟类名和冒号。按照惯例，类名使用驼峰式命名，例如 BankAccount 或 ExamResult。类的主体包含方法，即在类内部定义的函数。
A method must include self as its first parameter. The self parameter refers to the current instance and gives access to its attributes and other methods. When calling a method on an object, you do not pass self explicitly; Python does this automatically.
方法必须包含 self 作为其第一个参数。self 参数引用当前实例，并允许访问其属性和其他方法。在对象上调用方法时，你不必显式传入 self；Python 会自动完成。
class BankAccount:
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