1. 使用new方法

   class Singleton(object):
     def __new__(cls, *args, **kw):
       if not hasattr(cls, '_instance'):
         orig = super(Singleton, cls)
         cls._instance = org.__new__(cls, *args, **kw)
       return cls._instance
   class MyClass(Singleton):
     a = 1

2. 装饰器版本

   def singleton(cls):
    instances = {}
    def getinstance(*args, **kw):
        if cls not in instances:
            instances[cls] = cls(*args, **kw)
        return instances[cls]
    return getinstance
   
    @singleton
    class MyClass:
      ...

3. 加线程锁

   import threading
   class Singleton(object):
     _instance_lock = threading.Lock()  #添加类属性线程锁
   
     @classmethod
     def instance(cls, *args, **kw):
       with Singleton._instance_lock:  #创建实例时加线程锁，保证线程安全
         if not hasattr(Singleton, '_instance'):
           Singleton._instance = Singleton(*args, **kw)
       return Singleton._instance
   
   obj = Singleton.instance()
   print(obj)