python爬虫问题出错原因求助

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