def send_message(self, author, content):
        """发送私信给一个用户

        :param Author author: 接收私信用户对象
        :param string content: 发送给用户的私信内容
        :return: 成功返回 True，失败返回 False
        :rtype: bool
        """
        if isinstance(author, Author) is False:
            raise ValueError('argument answer need to be Zhihu.Author object.')
        if not content:
            raise ValueError('answer content cannot be empty')
        if author.url == self.url:
                return False
        data = {
            'member_id': author.hash_id,
            'content': content,
            'token': '',
            '_xsrf': author.xsrf
        }
        res = self._session.post(Send_Message_Url,
                                 data=data)
        return res.json()['r'] == 0
发送私信给一个用户

        :param Author author: 接收私信用户对象
        :param string content: 发送给用户的私信内容
        :return: 成功返回 True，失败返回 False
        :rtype: bool