def get(self, user_id=None):
if user_id is None:<EOL><INDENT>res = self._get(<EOL>'<STR_LIT>',<EOL>result_processor=lambda x: x['<STR_LIT>']<EOL>)<EOL><DEDENT>else:<EOL><INDENT>res = self._post(<EOL>'<STR_LIT>',<EOL>data={'<STR_LIT>': user_id},<EOL>result_processor=lambda x: x['<STR_LIT>']<EOL>)<EOL><DEDENT>return res<EOL>
查询所有分组或查询用户所在分组 ID

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

:param user_id: 用户 ID，提供时查询该用户所在分组，否则查询所有分组
:return: 所有分组列表或用户所在分组 ID

使用示例::

    from wechatpy import WeChatClient

    client = WeChatClient('appid', 'secret')
    group = client.group.get('openid')