如何在现有列表中添加字母等级？

Question

我需要将字母成绩添加到一个现有的列表中，这个列表中有学生ID和学生积分，范围是0-100.我认为我需要将字母成绩追加到列表中，但我甚至还不知道如何将数字转换为字母成绩。

student_grades = []
for i in range(0,20):
    student_grades.append(s[i])

for student in student_grades:
    Data = student.split("\t")
    letter_grade = Data[1]

if (80 <= Data <= 100):
    letter_grade = 'A'
elif (65 <= Data <= 79):
    letter_grade = 'B'
elif (50 <= Data <= 64):
    letter_grade = 'C'
elif (35 <= Data <= 49):
    letter_grade = 'D'
else:
    letter_grade = 'F'
print(letter_grade)

但每次我尝试运行它，用不同的if语句变化，程序的反应是--------。TypeError: '<=' not supported between instances of 'int' and 'str'

编辑：有没有更有效的方法？我的工作簿告诉我，我需要 "定义一个函数，它根据学生的标记计算学生的字母等级。也就是在参数中传递的分数，它返回相应的字母（作为一个字符串）。换算依据如下表格：A 80 - 100B 65 - 79C 50 - 64D 35 - 49E 0 - 34。

Answer 1

@Grismar和@revliscano指出了关于数据类型int和str的重要注意事项。这里有一个工作代码的例子。

student_grades = []
# This is a list of grade numbers. for example, `[20,17,61]`. I assume that you 
# store student names and ID and other information on another list.


# The following line of code will throw an exception if `student_grades` has 
# incorrect format
for x in student_grades:
    assert isinstance(x,(int,float))

# while `isinstance` is `python`'s built-in function to judge if `x` is of 
# type `int` or `float`, both are acceptable for grades.

def letter_grade(num):
    letter = None
    if num < 35:
        letter = 'F'
    elif num < 50:
        letter = 'D'
    elif num < 65:
        letter = 'C'
    elif num < 80:
        letter = 'B'
    else:
        letter = 'A'
    return letter
# Note how rewriting the cases make the conditions concise.


converted_grades = [letter_grade(num) for num in student_grades]
print(converted_grades)

现在我把它包在一个函数里，使它更容易使用.

def num_to_letter(nums):
    def letter_grade(num):
        letter = None
        if isinstance(num,(int,float)):
            if num < 35:
                letter = 'F'
            elif num < 50:
                letter = 'D'
            elif num < 65:
                letter = 'C'
            elif num < 80:
                letter = 'B'
            else:
                letter = 'A'
        return letter
    return [letter_grade(num) for num in nums]

一些测试。

print(num_to_letter([1,50,80]))
>> ['F', 'C', 'A']

print(num_to_letter([1,50,'invalid_score']))
>> ['F', 'C', None]

如果数据类型不正确，函数就会把字母等级保留为： None 而不抛出异常。