Python 类入门：定义、继承、封装与多态

学习目标：掌握类的定义、继承、封装、多态与魔术方法。

类与面向对象基础

2.1 类的定义

class Person:
    species = "Human"  # 类属性（所有实例共享）

    def __init__(self, name, age):  # 初始化方法
        self.name = name            # 实例属性
        self.age = age

    def greet(self):                # 实例方法
        return f"Hi, I'm {self.name}"

# 创建实例
p = Person("Alice", 25)
print(p.name)         # Alice
print(p.greet())      # Hi, I'm Alice
print(p.species)      # Human

2.2 继承

class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        raise NotImplementedError

class Dog(Animal):
    def speak(self):
        return f"{self.name}: Woof!"

class Cat(Animal):
    def speak(self):
        return f"{self.name}: Meow!"

dog = Dog("Buddy")
print(dog.speak())  # Buddy: Woof!

2.3 方法重写与 super()

class CocaCola:
    price = 3.5
    ingredients = ["caffeine", "sugar", "water", "soda"]

    def __init__(self, name):
        self.name = name

class CaffeineFree(CocaCola):
    """无咖啡因可乐，重写 ingredients"""
    ingredients = ["sugar", "water", "soda"]  # 重写类属性

    def __init__(self, name, ml):
        super().__init__(name)  # 调用父类初始化
        self.ml = ml

2.4 封装

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance  # 私有属性（双下划线开头）

    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount

    def get_balance(self):
        return self.__balance

2.5 多态

def animal_speak(animal):
    print(animal.speak())

animal_speak(Dog("Buddy"))   # Buddy: Woof!
animal_speak(Cat("Kitty"))   # Kitty: Meow!

2.6 魔术方法

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __str__(self):        # print() 时调用
        return f"Point({self.x}, {self.y})"

    def __repr__(self):       # 交互式环境中显示
        return f"Point({self.x}, {self.y})"

    def __eq__(self, other):  # == 比较
        return self.x == other.x and self.y == other.y

    def __add__(self, other): # + 运算
        return Point(self.x + other.x, self.y + other.y)

相关链接

• Python 面向对象编程 — OOP 进阶：property、综合案例
• Python 函数入门 — 函数定义与参数