Why do I get duplicate output when using a for loop over a list?

Question

Hello I have problem looping when printing data in a list.

def inputScore(scor) :
    for i in range(len(scor)) :
        scor[i] = int(input("Enter Score Number : "))

def Display(scr) :
    for i in scr:
        if i >= 86 and i <= 100 :
            x = "A"
        elif i >= 70 and i < 86 :
            x = "B"
        elif i >= 60 and i < 70 :
            x = "C"
        elif i >= 50 and i < 60 :
            x = "D"
        elif i >= 0 and i < 50 :
            x = "E"
        else :
            print("Invalid Score")
        for i in range(0,3) : # If I remove this code "for..", it will error "IndexError: list index out of range"
            print("Score Number",scr[i],"Letter Grades", x)

def main () :
    scor = [int]*3
    inputScore(scor)
    Display(scor)
main()

Example:

# Input :
85
60
40

# Output that I want :
Score Number 85 Letter Grades A
Score Number 60 Letter Grades C
Score Number 40 Letter Grades E

# Output that I got :
Score Number 85 Letter Grades A
Score Number 60 Letter Grades A
Score Number 40 Letter Grades A

Score Number 85 Letter Grades C
Score Number 60 Letter Grades C
Score Number 40 Letter Grades C

Score Number 85 Letter Grades E
Score Number 60 Letter Grades E
Score Number 40 Letter Grades E

There are 3 looping for Letter Grades (A = 3 times, C = 3 times and E = 3 times), I tried to give for i in range(0,3) for stop looping but it doesn't work, Letter Grades always prints 9 times with 3 A, 3 C, and 3 E. How to solve it and make it output like in the example above?

It’s good time to try debug this program yourself to learn the logic - pythontutor.com. — Daniel Hao
– Daniel Hao, Commented Jan 3, 2021 at 3:40

costaparas · Accepted Answer · 2021-01-03 03:48:35Z

The inner for loop is unnecessary. The outer for loop already iterates through the scores. In each iteration, i is a score, not an index -- to get an index, you use range. Therefore, there's no need to index the scr list at all -- you would print i itself rather than scr[i].

Also, with the current code, the grade for 85 would be B rather than A. Perhaps you need to adjust the bounds for the A and B grades.

Another issue is that for an invalid score, it would still attempt the final print. This would fail if an invalid score occurred as the first score (since x wouldn't be defined). If an invalid score occurred as a subsequent score, the print would show you the grade for the previous score, which you don't want. You can get around this by setting x to be the empty string at the start of each iteration and checking if it has a non-empty value before doing the final print of the grade.

The following code resolves the issues discussed:

def inputScore(scor):
    for i in range(len(scor)):
        scor[i] = int(input("Enter Score Number: "))

def display(scr):
    for i in scr:
        x = ""
        if i >= 85 and i <= 100:
            x = "A"
        elif i >= 70 and i < 85:
            x = "B"
        elif i >= 60 and i < 70:
            x = "C"
        elif i >= 50 and i < 60:
            x = "D"
        elif i >= 0 and i < 50:
            x = "E"
        else:
            print("Invalid Score")
        if x:
            print("Score Number:", i, "Letter Grade:", x)

def main():
    scor = [int] * 3
    inputScore(scor)
    display(scor)

main()

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