使用装饰器创建单例模式

singletion_with_decorator.py

def singleton(cls):
    _instance = {}
    def wrapper():
        if cls not in _instance:
            _instance[cls] = cls()

        return _instance[cls]

    return wrapper

@singleton
class A(object):
    pass

@singleton
class B(object):
    pass

if __name__ == '__main__':
    a1 = A()
    a2 = A()
    assert id(a1) == id(a2)
    b1 = B()
    b2 = B()
    assert id(b1) == id(b2)