def save_image(self, image):
        image_id = str(image.identifier)
        metadata = self._from_mongo_meta(self.collection.find_one( { "_id": image_id } ))
        if not metadata:
            raise ImageFactoryException('Image %s not managed, use "add_image()" first.' % image_id)
        self._save_image(image)
add to another list-like object
dataset/ETHPy150Open redhat-imaging/imagefactory/imgfac/MongoPersistentImageManager.py/MongoPersistentImageManager.save_image--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/django/contrib/gis/geos/mutable_list.py/ListMixin.__radd__