namedsingleton.py

class NamedSingletonMeta(type):
    def __new__(mcs, name, bases, dict):
        tp = type.__new__(mcs, name, bases, dict)
        if name != 'NamedSingletonBase':
            tp._instances = {}
        return tp

    def __getitem__(self, i):
        return self._instances[i]

    def __contains__(self, i):
        return i in self._instances

    def __setitem__(self, i, v):
        self._instances[i] = v

    def get(self, k, d=None):
        return self._instances.get(k, d)

    def clear(self):
        self._instances.clear()

    __getattr__ = __getitem__

class NamedSingletonBase(object, metaclass=NamedSingletonMeta):
    def __new__(mcs, name, *args, **kwargs):
        inst = mcs.get(name)
        if inst is None:
            inst = object.__new__(mcs)
            mcs[name] = inst
        return inst

    def __init__(self, name):
        self.name = name

    @classmethod
    def convert(cls, nm, create=False):
        if isinstance(nm, cls):
            return nm
        if create:
            return cls(nm)
        return cls[nm]

class NamedSingleton(NamedSingletonBase):
    pass