flask使用session保存登录状态及拦截未登录请求代码

<form action="/user/add" method="get"> 
    <input type="text" name="username" value="111"> 
    <input type="submit" value="提交"> 
</form> 

@user.route('/add',methods=['GET']) 
def add(): 
  username=request.values.get('username'); 
  session['username']=username 
  return session['username'] 

request.values.get('username'); 

s_option = request.values.getlist("s_option") 
for s in s_option: 
  pass 

@user.before_request 
def before_user(): 
  if 'username' in session: 
    return '已登录' 
    pass 
 else: 
    return '未登录'