文章标题

单例模式

代码如下:

class Singleton(object):
    __instance = None
    __first_init = False
    def __new__(cls, age, name):
        if cls.__instance is None:#等价于if not cls.__instance:
            cls.__instance = object.__new__(cls)
        return cls.__instance
    def __init__(self, age, name):
        if self.__first_init is False:#等价于if not self.__first_init:
            self.age = age
            self.name = name
            Singleton.__first_init = True

#创建对象a
a = Singleton(18, "xiaoMing")
#创建对象b
b = Singleton(19, "xiaoHong")
#分别打印a和b的地址,会发现是一样的
print(id(a))
print(id(b))
print(a.age, a.name)
print(b.age, b.name)
a.age = 19
print(b.age)

运行结果:

139901365269008
139901365269008
(18, 'xiaoMing')
(18, 'xiaoMing')
19

显然单例模式的要点有三个；一是某个类只能有一个实例；二是它必须自行创建这个实例；三是它必须自行向整个系统提供这个实例。