Python实现单例模式的四种方法

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

# 使用
singleton1 = Singleton()
singleton2 = Singleton()

# 检验
assert singleton1 is singleton2  # 为True，说明singleton1和singleton2是同一个实例

def singleton(cls):
    instances = {}
    def get_instance(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return get_instance

@singleton
class MyClass:
    pass

# 使用
my_class1 = MyClass()
my_class2 = MyClass()

# 检验
assert my_class1 is my_class2  # 为True，说明my_class1和my_class2是同一个实例

class SingletonBase:
    _instances = {}
    def __new__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(SingletonBase, cls).__new__(cls, *args, **kwargs)
        return cls._instances[cls]

class MyClass(SingletonBase):
    pass

# 使用
my_class1 = MyClass()
my_class2 = MyClass()

# 检验
assert my_class1 is my_class2  # 为True，说明my_class1和my_class2是同一个实例