Python 笔记之单例

#单例模式：只产生一次地址
#开发模式：单例模式

class singleleton:
    #私有化当前实例(对于内存的优化，保持地址)
    #单例的地址就存在于__instance中
    __instance=None
    name='jack'
    #重写__new__
    def __new__(cls):
        print('__new__')
        if cls.__instance is None:
            print('是空')
            cls.__instance=object.__new__(cls)
            print(cls.__instance)
            return cls.__instance
        else:
            print('不是空')
            return cls.__instance
    def show(self,n):
        print('--->show {0} is {1}'.format(self.name,n))
print(dir(singleleton))#查看类中所有的attribute
s=singleleton()
s1=singleleton()
print(s)
print(s1)
s.show(5)
s1.show(7)

输出：

'__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_singleleton__instance', 'name', 'show'

new

是空

<main.singleleton object at 0x000001D38C2F7130>

new

不是空

<main.singleleton object at 0x000001D38C2F7130>

<main.singleleton object at 0x000001D38C2F7130>

--->show jack is 5

--->show jack is 7