课程 20：类（Class）

1. 类与对象基础

1.1 类和对象的现实意义与历史

1.2 类的定义与实例化

# 定义类和创建对象
class Student:
    def __init__(self, name, score):
        self.name = name
        self.score = score
stu = Student('Alice', 95)
print(stu.name, stu.score)

2. 属性与方法细化

2.1 实例属性、类属性、私有属性

class Student:
    school = 'YunfanEdu'  # 类属性
    def __init__(self, name, score):
        self.name = name      # 实例属性
        self._secret = '私有数据'  # 约定私有属性
stu = Student('Bob', 88)
print(stu.name, stu.school)
print(stu._secret)  # 不建议外部访问

2.2 方法类型：实例方法、类方法、静态方法

class Demo:
    def instance_method(self):
        print('实例方法')
    @classmethod
    def class_method(cls):
        print('类方法')
    @staticmethod
    def static_method():
        print('静态方法')
d = Demo()
d.instance_method()
Demo.class_method()
Demo.static_method()

2.3 属性封装与getter/setter

class Person:
    def __init__(self, age):
        self._age = age
    @property
    def age(self):
        return self._age
    @age.setter
    def age(self, value):
        if value < 0:
            raise ValueError('年龄不能为负')
        self._age = value
p = Person(18)
p.age = 20
print(p.age)

3. 魔法方法与调试技巧

3.1 __str__、__repr__、__eq__等

class Student:
    def __init__(self, name, score):
        self.name = name
        self.score = score
    def __str__(self):
        return f"Student({self.name}, {self.score})"
    def __eq__(self, other):
        return self.name == other.name and self.score == other.score
stu1 = Student('Alice', 95)
stu2 = Student('Alice', 95)
print(stu1)
print(stu1 == stu2)

4. 继承、多态、组合与高级OOP

4.1 继承与super()

class Animal:
    def speak(self):
        print('动物叫')
class Dog(Animal):
    def speak(self):
        super().speak()
        print('汪汪!')
d = Dog()
d.speak()

4.2 多态与鸭子类型

class Cat:
    def speak(self):
        print('喵喵!')
def animal_speak(animal):
    animal.speak()
for a in [Dog(), Cat()]:
    animal_speak(a)

4.3 组合与MRO

class Engine:
    def start(self):
        print('发动机启动')
class Car:
    def __init__(self):
        self.engine = Engine()  # 组合
    def drive(self):
        self.engine.start()
        print('汽车行驶')
car = Car()
car.drive()
print(Car.__mro__)

5. 类的实际应用案例

5.1 学生成绩管理

class Student:
    def __init__(self, name):
        self.name = name
        self.scores = {}
    def add_score(self, subject, score):
        self.scores[subject] = score
    def show_all(self):
        print(f"{self.name}的成绩:")
        for subject, score in self.scores.items():
            print(f"  {subject}: {score}")
stu = Student('Alice')
stu.add_score('Math', 95)
stu.add_score('English', 88)
stu.show_all()

5.2 银行账户与工厂模式

class Account:
    def __init__(self, owner, balance=0):
        self.owner = owner
        self.balance = balance
    def deposit(self, amount):
        self.balance += amount
    def withdraw(self, amount):
        if amount > self.balance:
            print('余额不足')
        else:
            self.balance -= amount
class AccountFactory:
    @staticmethod
    def create_account(owner):
        return Account(owner)
acc = AccountFactory.create_account('Tom')
acc.deposit(100)
print(acc.balance)

5.3 图形类与方法扩展

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height
    def area(self):
        return self.width * self.height
    def perimeter(self):
        return 2 * (self.width + self.height)
    def is_square(self):
        return self.width == self.height
rect = Rectangle(3, 4)
print('面积:', rect.area())
print('周长:', rect.perimeter())
print('是否正方形:', rect.is_square())

6. 常见错误与调试

# __str__和__repr__调试
class Demo:
    def __repr__(self):
        return ''
print(Demo())
# isinstance判断
print(isinstance(rect, Rectangle))

7. 编程练习与挑战

8. 综合作业与项目