TypeError:python中/:“str”和“int”的操作数类型不受支持

我正在做一个项目,寻找学生三次考试的平均成绩。

我的工作似乎一切都很好,但有一个错误我收到了以下行:

student_avg = ((firstterm) +str (midterm) +str (final)) / 3 

该程序是讲师的配套应用程序。我的教授告诉我要做5门科目的第一学期期中和期末考试。

工作一周后,我在这方面仍然面临一些问题。 有人能检查一下我的代码,看看我的错误是什么吗?

def determine_score(grade):
    if 95<= grade <=100:
        return 'A+'
    elif 91<= grade <=96:
        return 'A'
    elif 89<= grade <=92:
        return 'A-'
    elif 85<= grade <=90:
        return 'B+'
    elif 81<= grade <=86:
        return 'B'
    elif 79<= grade <=82:
        return 'B-'
    elif 75<= grade <=80:
        return 'C+'
    elif 72<= grade <=76:
        return 'C'
    elif 64<= grade <=73:
        return 'D'
    elif 0<= grade <=65:
        return 'F'
    else:
        return 'invalide score'

def firstTerm():
    fst_sub1=int(input("Enter first term marks of the first subject: "))
    fst_sub2=int(input("Enter first term marks of the second subject: "))
    fst_sub3=int(input("Enter first term marks of the third subject: "))
    fst_sub4=int(input("Enter first term marks of the fourth subject: "))
    fst_sub5=int(input("Enter first term marks of the fifth subject: "))
    firsttermScore = (fst_sub1+fst_sub2+fst_sub3+fst_sub4+fst_sub5)/5
    return 'firsttermScore'

def midTerm():
    mid_sub1=int(input("Enter mid term marks of the first subject: "))
    mid_sub2=int(input("Enter mid term marks of the second subject: "))
    mid_sub3=int(input("Enter mid term marks of the third subject: "))
    mid_sub4=int(input("Enter mid term marks of the fourth subject: "))
    mid_sub5=int(input("Enter mid term marks of the fifth subject: "))
    midtermScore = (mid_sub1+mid_sub2+mid_sub3+mid_sub4+mid_sub5)/5
    return 'midtermScore'

def final():
    fnl_sub1=int(input("Enter final marks of the first subject: "))
    fnl_sub2=int(input("Enter final marks of the second subject: "))
    fnl_sub3=int(input("Enter final marks of the third subject: "))
    fnl_sub4=int(input("Enter final marks of the fourth subject: "))
    fnl_sub5=int(input("Enter final marks of the fifth subject: "))
    finalScore = (fnl_sub1+fnl_sub2+fnl_sub3+fnl_sub4+fnl_sub5)/5
    return 'finalScore'

total = 0
highest = 0
numStudents = int (input("How Many Students are there? "))
while numStudents < 0 or numStudents > 100:
    numStudents = int (input("Please enter a number between 0 and 100? "))

for i in range (numStudents):
    student_name = (input("Enter Student's Name Please: "))
    firstterm = firstTerm()
    midterm = midTerm()
    final = final()
    student_avg = ((firstterm) +str (midterm) +str (final)) / 3 
    if (highest < student_avg):
        highest = student_avg
        grade = student_avg  
        winner = student_name
        list_marks = []
        list_marks.append([student_name, student_avg,])
        print ("exam result: ", list_marks, "grade is: ", determine_score(grade))


print ("The Student with the higgest average is: ", winner, "With the highest average of: ", highest, "gpa is: " + determine_score(grade) )