def add_videos_to_playlist(self, access_token, playlist_id, video_ids):
        """doc: http://open.youku.com/docs/doc?id=75
        """
        url = 'https://openapi.youku.com/v2/playlists/video/add.json'
        data = {
            'client_id': self.client_id,
            'access_token': access_token,
            'playlist_id': playlist_id,
            'video_ids': video_ids
        }
        r = requests.post(url, data=data)
        check_error(r)
        return r.json()['id']
doc: http://open.youku.com/docs/doc?id=75