def get_group_id(self, user_id):
res = self._post(<EOL>'<STR_LIT>',<EOL>data={'<STR_LIT>': user_id},<EOL>result_processor=lambda x: x['<STR_LIT>']<EOL>)<EOL>return res<EOL>
获取用户所在分组 ID

详情请参考
http://mp.weixin.qq.com/wiki/0/56d992c605a97245eb7e617854b169fc.html

:param user_id: 用户 ID
:return: 用户所在分组 ID

使用示例::

    from wechatpy import WeChatClient

    client = WeChatClient('appid', 'secret')
    group_id = client.user.get_group_id('openid')