Python Day 74 单例模式总结

　　##基于classmethod

class Mysql(object):
    _instance =None
    def __init__(self,host,port):
        self.host = host
        self.port = port
    @classmethod
    def singleton(cls):
        if not cls._instance:
            cls._instance=cls('127.0.0.1',8000)
        return cls._instance
obj1=Mysql.singleton()
obj2=Mysql.singleton()
obj3=Mysql('192.168.10.1',3306)
print(id(obj1),id(obj2),id(obj3)) #1475724158400 1475724158400 1475724160304

　　##基于装饰器

def singelton(cls):
    _instance = cls('127.0.0.1',8000)#先对传入的类实例化一个对象
    def inner(*args,**kwargs):
        if args or kwargs:
            obj = cls(*args,**kwargs)
            return obj
        return _instance
    return inner
@singelton   #相当于 Mysql = singelton(Mysql)=inner
class Mysql(object):
    def __init__(self,host,port):
        self.host = host
        self.port = port
obj1 = Mysql()
obj2 = Mysql()
obj3=Mysql('192.168.1.1',3306)
print(id(obj1),id(obj2),id(obj3))#1744683247040 1744683247040 1744683249112