Python关于学生类成绩的排序

用字典保存学生对象，参考如下代码：

import csv
# import pandas pd
reader=csv.reader(open('score1.csv','r',encoding='utf-8'))
students={}
next(reader)
levels=lambda x:'A' if int(x)>=90 else 'B' if int(x)>=80 else 'C' if int(x)>=70 else 'D' if int(x)>=60 else 'F'
for r in reader:
    dg=levels(r[-1])
    students[r[1]]=r[2:]+[dg]    
print(students)
lst=[]
for k,v in students.items():
    lst.append([k]+v)
lst.sort(key=lambda x:x[-2])
print(lst)
for a in lst:
    print(*a,sep=' ')