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。