python 单例代码块

加锁

但是使用类方式创建的单例，无法支持多线程,因此使用加锁的方式;

未加锁部分并发执行,加锁部分串行执行,速度降低,但是保证了数据安全

import threading
class Singleton(object):
    _instance_lock = threading.Lock()
    def __init__(self):
        pass

    def __new__(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            with Singleton._instance_lock:
                if not hasattr(Singleton, "_instance"):
                    Singleton._instance = object.__new__(cls)
        return Singleton._instance