metaclass_registry_factory.py

def get_registry_metaclass(registry_name, class_name="MetaRegistry"):

  registration_method_name = 'register_class'

  def new(meta, name, bases, class_dict):
    cls = type.__new__(meta, name, bases, class_dict)
    if name not in getattr(meta, registry_name):
      getattr(meta, registration_method_name)(getattr(meta, registry_name), cls)
    return cls

  def register_class(registry, target_class):
    registry[target_class.__name__] = target_class

  return type(class_name, (type,), {registry_name: {}, 
                                         "__new__": new,
                                         registration_method_name: staticmethod(register_class)})