我需要更改我的代码，使其显示从最高到最低

Question

到目前为止，在我的代码中，我已经完成了它，以便显示平均值，并且可以按字母顺序对学生进行排序。但是，我需要更改我的代码，以便结果可以从最高到最低存储，但我正在努力解决这个问题。

在我的文本文件中，它看起来像这样： 名，3,4,5
2name，5,6,7
3name，3,4,5

每个名称不同

到目前为止，这是我的代码：

class Student:
    def __init__(self, name, marks):
        self.name = name
        self.marks = marks
    def avg_mark(self):
        return sum(self.marks)/len(self.marks)
    def __str__(self):
        return '{0}: {1}, {2}'.format(self.name, self.marks,     self.avg_mark())

def load_grades(filename):
    fd = open(filename, 'r')
    f = {}
    for line in fd:
        split = line.split(',')
        key = split[0]
        marks = [int(n) for n in split[1:]]
        try:
           f[key] += marks
        except KeyError:
            f[key] = marks
    students = []
    for key, values in f.items():
        students.append(Student(key, values[-3:]))
    return students

def sort_by_name(students):
    def get_name(student):
      return student.name
    students = sorted(students, key=get_name)
    return students

def sort_by_avg(students):
    def get_avg(student):
        return student.avg_mark()
    students = sorted(students, key=get_avg)
    return students


again = True

while again:
    class_num =  input ('Which class do you want to view 1,2 or 3?')
    print('please input a, b or c')
    print('a)Alphabeically')
    print('b)average')
    print('c)highest to lowest')
    sort = input ('how would you like to view it:')

    if class_num =="1" and sort =="a":
        students = load_grades('class1.txt')
        students = sort_by_name(students)
    elif class_num =="1" and sort =="b":
        students = load_grades('class1.txt')
        students = sort_by_avg(students)

    for student in students:
        print(student)


    Again=input('Do you want to view another class yes or no?')
    again = (Again=='yes')

print('bye')

我想要它，这样当按下c时，数字从最高到最低排序。

由于