def list_devices(self, shop_id=None, page_index=1, page_size=20):
        """
        查询设备

        详情请参考
        http://mp.weixin.qq.com/wiki/10/6232005bdc497f7cf8e19d4e843c70d2.html

        :param shop_id: 可选，门店 ID
        :param page_index: 可选，分页下标，默认从1开始
        :param page_size: 可选，每页的个数，默认20个，最大20个
        :return: 返回的 JSON 数据包
        """
        data = optionaldict(
            shop_id=shop_id,
            pageindex=page_index,
            pagesize=page_size
        )
        res = self._post(
            'device/list',
            data=data,
            result_processor=lambda x: x['data']
        )
        return res