列表被后面的覆盖了用的append()不知道怎么回事

填加的列表被覆盖了，前一个被后面的覆盖了
import requests
from bs4 import BeautifulSoup
import bs4
def gethtmltxt():
try:
kv = {'User-Agent': "Mozilla/5.0"}
r = requests.get("https://www.eol.cn/e_html/gk/dxpm/index.shtml%22, headers=kv)
r.encoding = r.apparent_encoding
return r.text
except:
return "失败"

def ulist(ulist,html):
soup=BeautifulSoup(html,"html.parser")
for tr in soup.find('table').children:
if isinstance(tr, bs4.element.Tag):
tds = tr('td')
ulist.append([tds[0].string,tds[1].string,tds[2].string])
def printliebiao(ulist,num):
for i in range(num):
try:
u = ulist[i]

    except:
        print("第{}条存在问题".format(i+1))

def main():
uinfo=[]
html=gethtmltxt()
ulist(uinfo,html)
printliebiao(uinfo,20)
print(uinfo)
main()

代码看上去没什么问题啊
ulist.append([tds[0].string,tds[1].string,tds[2].string])
你在这后面打印一下列表ulist看看内容有什么变化