with requests.Session() as s:
req = s.get(url)
print("cookies="+repr(req.cookies))
html = req.text
user = re.findall(r'input\s+type="text"\s+class="sl"\s+name="(\S+)"',html)
key = re.findall(r'input\s+type="password"\s+class="sl"\s+name="(\S+)"',html)
once = re.findall(r'input\s+type="hidden"\s+value="(\S+)"\s+name="once"',html)
postdata = {user[0]:"uuuuuu",key[0]:"123456","once":once[0],"next":"/"}
print("data="+repr(postdata))

login_req = requests.post(url,headers=headers,data=postdata,cookies=req.cookies)

@linoder 你是指《推荐系统实践》吗？