def reply_topic(self, topic_id, content):
data = {<EOL>'<STR_LIT:body>': content,<EOL>'<STR_LIT>': self._request.cookies.get('<STR_LIT>')<EOL>}<EOL>url = '<STR_LIT>' % topic_id<EOL>r = self.request(url, '<STR_LIT>', data=data)<EOL>j = r.json()<EOL>if j['<STR_LIT>'] == <NUM_LIT:0>:<EOL><INDENT>return j['<STR_LIT:data>']['<STR_LIT>']['<STR_LIT:id>']<EOL><DEDENT>
小组回帖

        :return: 帖子 id 或 ``None``