### 封装、继承和多态的高级用法 #### 1. 封装的高级应用 封装不仅仅是隐藏数据成员，还涉及提供更复杂的访问控制机制。通过使用属性装饰器或自定义存取方法，可以在获取或修改字段时执行额外逻辑。 ```python class AdvancedEncapsulationExample: def __init__(self, value=0): self._value = value @property def value(self): # Getter method with additional logic print("Accessing the 'value' property.") return self._value @value.setter def value(self, new_value): # Setter method that includes validation if isinstance(new_value, int) and new_value >= 0: print(f"Setting 'value' to {new_value}.") self._value = new_value else: raise ValueError("'value' must be a non-negative integer.") example_instance = AdvancedEncapsulationExample() print(example_instance.value) # Output will include message about accessing. try: example_instance.value = -5 # This should trigger an exception due to invalid input. except ValueError as e: print(e) ``` #### 2. 继承中的抽象基类与多重继承 Python 支持多重继承以及通过 `abc` 模块创建抽象基类 (ABC)，这有助于强制实现特定的方法，并且能够更好地管理复杂层次结构下的代码复用问题。 ```python from abc import ABC, abstractmethod class AbstractBase(ABC): @abstractmethod def required_method(self): pass class Child(AbstractBase): def required_method(self): print('Implementation of required_method') child_instace = Child() child_instace.required_method() # Multiple Inheritance Example class FirstParent: def greet(self): print('Hello from First Parent') class SecondParent: def farewell(self): print('Goodbye from Second Parent') class MultiChild(FirstParent, SecondParent): pass multi_child_instance = MultiChild() multi_child_instance.greet() # Outputs greeting from first parent class multi_child_instance.farewell() # Outputs goodbye from second parent class ``` #### 3. 多态性的动态调度与鸭子类型 除了传统的基于类的关系来决定行为外，在 Python 中还可以利用所谓的“鸭子类型”，即只要某个对象实现了所需的操作接口就可被接受作为参数传递给其他函数而无需关心其确切的数据类型。这种灵活性使得开发者能够在不改变现有API的情况下轻松添加新功能模块。 ```python def make_sound(animal): animal.speak() class Dog: def speak(self): print('Woof!') class Cat: def speak(self): print('Meow!') doggy = Dog() kitty = Cat() make_sound(doggy) # Prints "Woof!" make_sound(kitty) # Prints "Meow!" # Polymorphic behavior using duck typing class DuckTypingExample: def quack(self): print("Quacking like a duck!") duck_like_object = DuckTypingExample() if hasattr(duck_like_object, 'quack') and callable(getattr(duck_like_object, 'quack')): make_sound(duck_like_object) ```