【Python篇】Python 类和对象：详细讲解（下篇）

from typing import Protocol

# 定义一个飞行协议，规定类必须有 fly 方法
class Flyer(Protocol):
    def fly(self) -> None:
        pass

# 定义一个 Bird 类，它实现了 fly 方法
class Bird:
    def fly(self) -> None:  # 注意 -> None 表示这个方法不返回任何值
        print("Bird is flying")

# 定义一个 Airplane 类，它也实现了 fly 方法
class Airplane:
    def fly(self) -> None:
        print("Airplane is flying")

# 定义一个函数，这个函数接受任何有 fly 方法的对象
def make_fly(flyer: Flyer):
    flyer.fly()

# 创建 Bird 和 Airplane 的实例，并传递给 make_fly 函数
bird = Bird()
plane = Airplane()

make_fly(bird)    # 输出: Bird is flying
make_fly(plane)   # 输出: Airplane is flying

Bird is flying
Airplane is flying

# 定义一个简单的装饰器函数
def simple_decorator(func):
    def wrapper():
        print("Something is happening before the function is called.")
        func()  # 调用原始函数
        print("Something is happening after the function is called.")
    return wrapper

# 使用装饰器
@simple_decorator  # @符号表示我们使用simple_decorator来装饰say_hello函数
def say_hello():
    print("Hello!")

# 调用被装饰的函数
say_hello()

Something is happening before the function is called.
Hello!
Something is happening after the function is called.

# 使用 @ 语法糖
@simple_decorator
def say_hello():
    print("Hello!")

# 不使用 @ 语法糖，等同于上面的代码
def say_hello():
    print("Hello!")
say_hello = simple_decorator(say_hello)

# 使用上下文管理器打开文件
with open('example.txt', 'w') as file:
    file.write('Hello, World!')

# 这个文件会在 with 语句块结束时自动关闭

class MyContextManager:
    def __enter__(self):
        print("Entering the context")
        return self
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Exiting the context")
        if exc_type:
            print(f"Exception type: {exc_type}")
            print(f"Exception value: {exc_val}")
            print(f"Traceback: {exc_tb}")
        return True  # 处理异常后，继续执行

# 使用自定义上下文管理器
with MyContextManager():
    print("Inside the context")
    raise ValueError("Oops!")  # 故意引发一个异常

Entering the context
Inside the context
Exiting the context
Exception type: <class 'ValueError'>
Exception value: Oops!
Traceback: <traceback object at 0x...>

class MyMeta(type):
    def __new__(cls, name, bases, dct):
        print(f"Creating class {name}")
        return super().__new__(cls, name, bases, dct)

class MyClass(metaclass=MyMeta):
    pass

# 创建 MyClass 的实例
obj = MyClass()

Creating class MyClass

class ReportGenerator:
    def generate(self):
        print("Generating report")

class ReportSaver:
    def save(self):
        print("Saving report")

class Shape:
    def area(self):
        pass

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

    def area(self):
        return 3.14 * (self.radius ** 2)

class Rectangle(Shape):
    def __init__(self, length, width):
        self.length = length
        self.width = width

    def area(self):
        return self.length * self.width

class Bird:
    def fly(self):
        print("Bird is flying")

class Penguin(Bird):
    def fly(self):
        raise NotImplementedError("Penguins cannot fly")

# 这种设计违反了里氏替换原则，因为企鹅不能飞，但它继承了能飞的鸟类

class Workable:
    def work(self):
        pass

class Eatable:
    def eat(self):
        pass

class Worker(Workable, Eatable):
    def work(self):
        print("Working")

    def eat(self):
        print("Eating")

class Robot(Workable):
    def work(self):
        print("Working")

# Robot 只实现了它需要的接口，而不是所有接口