def save(self):
        tmp_path = self.path + '.tmp'
        with open(tmp_path, 'w') as f:
            f.write(json.dumps(self.body_labels.items()))
        os.rename(tmp_path, self.path)
def setdefault(self, key, default=None):
        return self._collection.setdefault(key, self._from_python(key, default))