python爬虫问题出错原因求助

Question

import requests
from bs4 import BeautifulSoup
import bs4

def getHTMLText(url):
try:
r = requests.get(url, timeout=30)
r.raise_for_status()
r.encoding = r.apparent_encoding
return r.text
except:
return ""

def fillUnivList(ulist, html):
soup = BeautifulSoup(html, "html.parser")
for tr in soup.find('tbody').children:
if isinstance(tr, bs4.element.Tag):
tds = tr('td')
ulist.append([tds[0].string, tds[1].string, tds[3].string])

def printUnivList(ulist, num):
print("{:^10}\t{:^6}\t{:^10}".format("排名","学校名称","总分"))
for i in range(num):
u=ulist[i]
print("{:^10}\t{:^6}\t{:^10}".format(u[0],u[1],u[2]))

def main():
uinfo = []
url = 'http://www.zuihaodaxue.cn/zuihaodaxuepaiming2017.html'
html = getHTMLText(url)
fillUnivList(uinfo, html)
printUnivList(uinfo, 20) # 20 univs
main()

出错为：Traceback (most recent call last):
File "D:/python02/01/11.py", line 34, in
main()
File "D:/python02/01/11.py", line 33, in main
printUnivList(uinfo, 20) # 20 univs
File "D:/python02/01/11.py", line 26, in printUnivList
print("{:^10}\t{:^6}\t{:^10}".format(u[0],u[1],u[2]))
TypeError: unsupported format string passed to NoneType.__format__
第一次爬虫，不是很能理解出错原因。求指教

Answer 1

python的爬虫经常会爬取到none这种节点，当你获取的节点是none，还要继续对它进行操作的时候就会报错，这种问题只能是小心翼翼地判断每个读到的节点是什么类型，建议你对照要爬的页面的结构并且在代码中打印获取到的节点类型以及内容等，结合起来判断会比较有帮助