单例类

Python中的有且只能有一个实例化对象的一种类。实现方法很多，这里列举两个：

实例1：__new__方法

class SingleClass(object):

    def __new__(cls):
        if not hasattr(cls, "instance"):
            cls.instance = super(SingleClass, cls).__new__(cls)
        return cls.instance


if __name__ == '__main__':
    a = SingleClass()
    b = SingleClass()
    print(a)
    print(b)

结果：

<__main__.SingleClass object at 0x000001C8749C3F28>
<__main__.SingleClass object at 0x000001C8749C3F28>

Process finished with exit code 0

实例2：自定义属性判断

class SingleClass(object):
    __instance = None  # 自定义一个类属性做判断

    def __new__(cls, *args, **kwargs):
        if cls.__instance == None:
            '''
            如果__instance为空，证明是第一次创建实例
            通过父类的__new__方法创建实例
            '''
            cls.__instance = object.__new__(cls)
            return cls.__instance
        else:
            # 返回上一个对象的引用
            return cls.__instance


a = SingleClass()
b = SingleClass()
print(a)
print(b)

结果：

<__main__.SingleClass object at 0x0000020E17B63F28>
<__main__.SingleClass object at 0x0000020E17B63F28>

Process finished with exit code 0