src/transformers/models/realm/retrieval_realm.py/RealmRetriever/save_pretrained
class RealmRetriever:    def save_pretrained(self, save_directory):
        # save block records
        np.save(os.path.join(save_directory, _REALM_BLOCK_RECORDS_FILENAME), self.block_records)
        # save tokenizer
        self.tokenizer.save_pretrained(save_directory)