python 单例模式实现

def singleton(cls, *args, **kw):
    instances = {}

    def _singleton():
        key = str(cls) + str(os.getpid())
        if key not in instances:
            instances[key] = cls(*args, **kw)
        return instances[key]
    return _singleton

@singleton
class mytest:
    def __init__(self):
        self.a='1'