单例模式

单例模式：

class MySocketClient:
    __instance = None

    # 单例模式（同一时间只有一个实例）
    def __new__(cls, *args, **kwargs):
        if MySocketClient.__instance is None:
            MySocketClient.__instance = object.__new__(cls, *args, **kwd) #object.__new__ 实例化
            ip_port = (configuration.get('server_ip'), configuration.get('server_port'))
            cls.sk = socket.socket()
            cls.conn = cls.sk.connect(ip_port)
        return MySocketClient.__instance

　　如果MySocketClient.__instance为原始值，就对MySocketClient类进行实例化（object.__new__(cls, *args, **kwd)）并赋值给MySocketClient.__instance，

4.基于__new__方法实现的单例模式(推荐使用,方便)

1> 一个对象的实例化过程是先执行类的__new__方法,如果我们没有写,默认会调用object的__new__方法,返回一个实例化对象,然后再调用__init__方法,对这个对象进行初始化,我们可以根据这个实现单例.
2> 在一个类的__new__方法中先判断是不是存在实例,如果存在实例,就直接返回,如果不存在实例就创建.

# encoding:utf-8
__author__ = 'Fioman'
__time__ = '2020/5/26 12:36'
import threading


class Singleton(object):
    _instance_lock = threading.Lock()

    def __init__(self, *args, **kwargs):
        pass

    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            with Singleton._instance_lock:
                if not hasattr(cls, '_instance'):
                    Singleton._instance = super().__new__(cls)

            return Singleton._instance


obj1 = Singleton()
obj2 = Singleton()
print(obj1, obj2)


def task(arg):
    obj = Singleton()
    print(obj)


for i in range(10):
    t = threading.Thread(target=task, args=[i, ])
    t.start()