class Singleton(type):
    _instances = {}

    def __call__(cls, *args, **kwargs):
        //make name change here
        if cls not in cls._instances:
            cls._instances[cls] = super(
                Singleton,
                cls).__call__(
                *args,
                **kwargs)
        return cls._instances[cls]

_STAGE = Singleton("_STAGE", (object, ), {})

PoolManager(_STAGE):
  ...