Python ABC to register subclasses with a name for easy retrieval.

namedregistry.py

class NamedRegistry(ABCMeta):
    '''
    A metaclass which automatically registers each subclass by name when it is
    defined.

    Each subclass must define the class-attribute ``NAME``

    The classes can be retrieved using ``NamedRegistry.get_query``.
    '''

    GLOBAL_REGISTRY = {}  # type: Dict[type, Dict[str, type]]
    __DISCRIMINATOR = None

    def __new__(mcs, name, bases, namespace, **kwargs):
        cls = super().__new__(mcs, name, bases, namespace, **kwargs)

        # Without a discriminator it would not be possible to have two separete
        # subclass trees using the registry
        if cls.__DISCRIMINATOR is None:
            cls.__DISCRIMINATOR = cls

        # We don't want the top-level class to show up in the registry. We can
        # use the discriminator we used earlier for that.
        if cls.mro()[0] == cls.__DISCRIMINATOR:
            return cls

        registry = NamedRegistry.GLOBAL_REGISTRY.setdefault(cls.__DISCRIMINATOR, {})
        if cls.NAME in registry:
            raise KeyError(
                'The name %r for class %r has already been registered. '
                'Please use another name!' % (cls.NAME, cls))
        registry[cls.NAME] = cls
        return cls

    def get_query(cls, name: str):
        '''
        Retrieves a class by defined name.
        '''
        return NamedRegistry.GLOBAL_REGISTRY[cls][name]

    def all(cls):
        '''
        Return all registered classes under *cls*
        '''
        return NamedRegistry.GLOBAL_REGISTRY[cls].values()