__new__ 单例

a.实例化类

实例化一个类时
1. 创建一个对象,调用__new__方法,如果没有会调用父类的__new__方法
2. 调用__init__方法
3. 返回对象的引用

class Dog(object):
    def __init__(self):
        print("---init方法---")    def __new__(cls, *args, **kwargs):
        print("---new方法---")xtq = Dog()#---------结果---------    ---new方法---

b. 单例

class Dog(object):    _instance = None
    _init_flag = False    def __new__(cls, *args , **kwargs): #cls指向Dog
        if cls._instance == None:
            cls._instance = object.__new__(cls)
            return cls._instance
        else:
            return cls._instance    def __init__(self,name):
        if Dog._init_flag == False:
            self.name = name
            Dog._init_flag = Truea = Dog("旺财")
print(a.name)
b = Dog("啸天犬")
print(b.name)#----------------结果-----------------
旺财
旺财