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 commit(self):
        context = self.pop()
        if self:
            # savepoint
            self[-1]['cbs'].extend(context['cbs'])
            self[-1]['dirty'] = self[-1]['dirty'] or context['dirty']
        else:
            # transaction
            for func, args, kwargs in context['cbs']:
                func(*args, **kwargs)