def __init__(self, cid, answer, author,<EOL>upvote_num, content, time, group_id=None):
self.cid = cid<EOL>self.answer = answer<EOL>self.author = author<EOL>self.upvote_num = upvote_num<EOL>self.content = content<EOL>self.creation_time = time<EOL>self._group_id = group_id<EOL>
创建评论类实例.

        :param int cid: 评论ID
        :param int group_id: 评论所在的组ID
        :param Answer answer: 评论所在的答案对象
        :param Author author: 评论的作者对象
        :param int upvote_num: 评论赞同数量
        :param str content: 评论内容
        :param datetime.datetime creation_time: 评论发表时间
        :return: 评论对象
        :rtype: Comment