单例模式

# 实例化一个单例
class Singleton(object):
    __instance = None
    __is_first = True
def __new__(cls, age, name):
    if not cls.__instance:
        cls.__instance = object.__new__(cls)
        return cls.__instance
def __init__(self, age, name):
    if self.__is_first:
        self.age = age
        self.name = name
        Singleton.__is_first = False
a = Singleton(18, "周润发")
b = Singleton(28, "周星驰")
print(id(a))
print(id(b))
print(a.age)
print(b.age)
a.age = 19
print(b.age)