如何创建/访问类的实例

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

    def greet(self):
        return f"Hello, {self.name}!"

# 创建类的实例
instance = MyClass("World")

# 访问实例的属性和方法
print(instance.name)  # 输出: World
print(instance.greet())  # 输出: Hello, World!

class Singleton:
    _instance = None

    def __new__(cls, *args, **kwargs):
        if not cls._instance:
            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instance

# 测试单例模式
s1 = Singleton()
s2 = Singleton()
print(s1 is s2)  # 输出: True

class Product:
    def use(self):
        pass

class ConcreteProductA(Product):
    def use(self):
        return "Using Product A"

class ConcreteProductB(Product):
    def use(self):
        return "Using Product B"

class Creator:
    def factory_method(self):
        return ConcreteProductA()

    def some_operation(self):
        product = self.factory_method()
        result = f"Creator: The same creator's code has just worked with {product.use()}"
        return result

class ConcreteCreator1(Creator):
    def factory_method(self):
        return ConcreteProductB()

# 使用工厂方法创建对象
creator = ConcreteCreator1()
print(creator.some_operation())  # 输出: Creator: The same creator's code has just worked with Using Product B