def create_comment(self, access_token, video_id, content,
                       reply_id=None, captcha_key=None, captcha_text=None):
        """doc: http://open.youku.com/docs/doc?id=41
        """
        url = 'https://openapi.youku.com/v2/comments/create.json'
        data = {
            'client_id': self.client_id,
            'access_token': access_token,
            'video_id': video_id,
            'content': content,
            'reply_id': reply_id,
            'captcha_key': captcha_key,
            'captcha_text': captcha_text
        }
        data = remove_none_value(data)
        r = requests.post(url, data=data)
        check_error(r)
        return r.json()['id']
doc: http://open.youku.com/docs/doc?id=41