求指点啊，为啥这个base-url在下面用不了

小李子-

import requests
from lxml import etree
url = 'https://music.163.com/playlist?id=2821115454'
base_url='http://link.hhtjim.com/163'
result = requests.get(url).text
dom = etree.HTML(result)
ids = dom.xpath('//a[contains(@href,"song?")]/@href')
for song_id in ids:
    count_id=song_id.strip('./song?id=')
    if ('$' in count_id) == False:
        song_url = base_url + '%s'count_id +'.mp3'
        song_name=song_url.split('/')[-1]
        print(song_name)
        music =requests.get(song_url).content
        with open('.wangyi/%s'%song_name,'wb') as file:
            file.write(music)

bozhen

song_url = base_url + '%s'count_id +'.mp3'  改成 song_url = base_url + '%s' %count_id +'.mp3'