python中单例模式的创建

# 单例模式（使用装饰器）
def singleton(cls):
    instance = {}

    def wrapper(*args,**kwargs):
        if cls not in instance:
            instance[cls] = cls(*args,**kwargs)
        return instance[cls]
    return wrapper

@singleton
class Foo(object):
    pass

foo1 = Foo()
foo2 = Foo()
print(foo1 is foo2)  # True


# 单例模式（使用基类）
class Singleton(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, ‘_instance‘):
            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instance
    
class Foo(Singleton):
    pass

foo1 = Foo()
foo2 = Foo()

print(foo1 is foo2)  # True