code: def register(self, model_or_iterable, opts_class=None, **options):
          
          if isinstance(model_or_iterable, ModelBase):
              model_or_iterable = [model_or_iterable]
  
          for model in model_or_iterable:
              # Ensure that a base is not registered after a subclass (_registry
              # is closed with respect to taking bases, so we can just check if
              # we've seen the model).
              if model in self._registry:
                  if self._registry[model].registered:
                      raise AlreadyRegistered(
                          'Model "%s" is already registered for translation' %
                          model.__name__)
                  else:
                      descendants = [d.__name__ for d in self._registry.keys()
                                     if issubclass(d, model) and d != model]
                      if descendants:
                          raise DescendantRegistered(
                              'Model "%s" cannot be registered after its subclass'
                              ' "%s"' % (model.__name__, descendants[0]))
  
              # Find inherited fields and create options instance for the model.
              opts = self._get_options_for_model(model, opts_class, **options)
  
              # If an exception is raised during registration, mark model as not-registered
              try:
                  self._register_single_model(model, opts)
              except Exception:
                  self._registry[model].registered = False
                  raise
docs: Registers the given model(s) with the given translation options.
  
          The model(s) should be Model classes, not instances.
  
          Fields declared for translation on a base class are inherited by
          subclasses. If the model or one of its subclasses is already
          registered for translation, this will raise an exception.