Python面向对象编程的封装艺术与实战示例-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_47267103/article/details/145975239

Python面向对象编程的封装艺术与实战示例

本文将深入探讨Python面向对象编程中的封装特性，通过10个层次递进的代码示例，揭示封装机制的核心原理与实践应用。读者将全面掌握如何通过封装构建健壮、安全的Python程序。

1. 封装基础：类与对象的保护屏障

class BankAccount:
    def __init__(self, owner, balance=0):
        self.owner = owner
        self._balance = balance  # 受保护属性

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

    def get_balance(self):
        return self._balance

# 使用示例
account = BankAccount("Alice", 1000)
account.deposit(500)
print(f"Current balance: {account.get_balance()}")  # 输出：Current balance: 1500

代码解析：

使用单下划线_balance约定为受保护属性
通过方法控制存款操作的合法性验证
提供专用方法访问敏感数据

2. 严格封装：私有属性实践

class TemperatureSensor:
    def __init__(self):
        self.__current_temp = 25  # 双下划线定义私有属性

    def __calibrate(self):        # 私有方法
        self.__current_temp += 0.5

    def get_temperature(self):
        self.__calibrate()
        return self.__current_temp

sensor = TemperatureSensor()
print(sensor.get_temperature())  # 输出：25.5
# print(sensor.__current_temp)   # 触发AttributeError

关键特性：

名称修饰（Name Mangling）实现伪私有化
隐藏内部实现细节
防止外部直接修改关键数据

3. 属性装饰器：智能访问控制

class Circle:
    def __init__(self, radius):
        self._radius = radius

    @property
    def radius(self):
        """半径属性读取器"""
        return self._radius

    @radius.setter
    def radius(self, value):
        if value <= 0:
            raise ValueError("Radius must be positive")
        self._radius = value

    @property
    def area(self):
        """动态计算属性"""
        return 3.14159 * self._radius ** 2

circle = Circle(5)
circle.radius = 7  # 自动调用setter验证
print(f"Area: {circle.area:.2f}")  # 输出：Area: 153.94

4. 继承中的封装保护

class Vehicle:
    def __init__(self):
        self.__engine_code = "V8-2024"  # 私有属性

    def _start_engine(self):      # 受保护方法
        print("Engine started")

class Car(Vehicle):
    def drive(self):
        self._start_engine()
        # print(self.__engine_code)  # 访问失败

car = Car()
car.drive()  # 输出：Engine started

5. 动态属性计算与缓存

class ShoppingCart:
    def __init__(self):
        self.__items = []
        self.__total = None

    def add_item(self, item, price):
        self.__items.append((item, price))
        self.__total = None  # 重置缓存

    @property
    def total(self):
        if self.__total is None:
            self.__total = sum(price for _, price in self.__items)
        return self.__total

cart = ShoppingCart()
cart.add_item("Book", 29.99)
cart.add_item("Mouse", 49.99)
print(f"Total: ${cart.total:.2f}")  # 输出：Total: $79.98

6. 上下文管理器封装资源

class DatabaseConnection:
    def __init__(self, conn_str):
        self.__conn_str = conn_str
        self.__connection = None

    def __enter__(self):
        self.__connection = connect(self.__conn_str)
        return self.__connection

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.__connection.close()
        print("Connection closed")

# 使用示例
with DatabaseConnection("localhost:5432") as conn:
    conn.execute("SELECT * FROM users")
# 自动关闭连接并输出：Connection closed

7. 多层级封装体系

class Employee:
    def __init__(self, name, salary):
        self.name = name
        self.__salary = salary
        self.__bonus = 0

    def __calculate_bonus(self):
        return self.__salary * 0.1

    def apply_bonus(self):
        self.__bonus = self.__calculate_bonus()

    @property
    def total_compensation(self):
        return self.__salary + self.__bonus

emp = Employee("Bob", 80000)
emp.apply_bonus()
print(f"Total compensation: ${emp.total_compensation}")  # 输出：Total compensation: $88000

8. 封装与单元测试

class LightSwitch:
    def __init__(self):
        self.__is_on = False

    @property
    def is_on(self):
        return self.__is_on

    def toggle(self):
        self.__is_on = not self.__is_on

# 测试用例
def test_light_switch():
    switch = LightSwitch()
    assert not switch.is_on
    switch.toggle()
    assert switch.is_on
    switch.toggle()
    assert not switch.is_on

9. 属性验证装饰器

def validate_age(func):
    def wrapper(self, value):
        if not 18 <= value <= 65:
            raise ValueError("Age must be between 18-65")
        return func(self, value)
    return wrapper

class Employee:
    def __init__(self, age):
        self.age = age

    @property
    def age(self):
        return self._age

    @age.setter
    @validate_age
    def age(self, value):
        self._age = value

# 使用示例
emp = Employee(30)
emp.age = 25  # 有效
# emp.age = 70  # 触发ValueError

10. 组合模式中的封装

class Computer:
    class __Processor:  # 内部类
        def __init__(self, model):
            self.model = model

        def execute(self):
            print(f"{self.model} processing...")

    def __init__(self):
        self.__processor = self.__Processor("Intel i9")

    def start(self):
        self.__processor.execute()

pc = Computer()
pc.start()  # 输出：Intel i9 processing...
# pc.__processor  # 无法直接访问