python 单例模式 一般实现方法

# 用户管理器
class UserManager(object):
    # 定义静态变量实例
    __instance = None
    __lock = threading.Lock()
 
    def __init__(self):
        pass
 
    def __new__(cls, *args, **kwargs):
        if not cls.__instance:
            try:
                UserManager.__lock.acquire()
                # double check
                if not cls.__instance:
                    cls.__instance = super(UserManager, cls).__new__(cls, *args, **kwargs)
            finally:
                UserManager.__lock.release()
        return cls.__instance

 

user_manager = UserManager()