Python list index is out of range error

Question

I've been tasked with making a Quiz app for a school project. It's meant to ask the user how many questions they want, and they then enter all of the Q&A's. Once finished, someone will then take the test.

The problem is, I'm getting an IndexError from the results function. This function is supposed to compare the test answers with the user's answers and print out a score.

def results(testAnswers, userAnswers):
    score = 0
    for i in range(0, len(answers)):
        if testAnswers[i].lower().strip() == userAnswers[i].lower().strip():
            score += 1

    print("\nResults: You got " + str(score) + " out of " + str(len(answers)) + "!")

Does anyone know how I can fix this problem?

As it is written in this question i don't think this can be your actual code, Can you please fix up the formatting so that it is the same as your program. — Serdalis
– Serdalis, Commented Oct 23, 2014 at 19:58
Please correct the indentation of your code. It is currently not possible to see what's going on here. — user740316
– user740316, Commented Oct 23, 2014 at 19:58
Sorry about my code indentation, the code that is above is my actual code. I am not sure what is wrong with it :( — Jonty Morris
– Jonty Morris, Commented Oct 24, 2014 at 5:24

karthikr · Accepted Answer · 2014-10-23 20:00:26Z

Your problem is here:

while n < times:
    if user_answers[n] == answer_list[n]:
        score += 1
        n += 1
    if user_answers[n] != answer_list[n]:
        n += 1

Lets say times is 10, and n is 9, it executes, and n+=1 makes it 10. Most likely, you have 10 elements in the array (note 10 is an example), and now user_answers[10 raises an exception, as the valid varles are 0..9

To fix this issue, use elif:

while n < times:
    if user_answers[n] == answer_list[n]:
        score += 1
        n += 1
    elif user_answers[n] != answer_list[n]:
        n += 1

Alternate approach is to get rid of the else clause altogether,

while n < times:
    if user_answers[n] == answer_list[n]:
        score += 1
    n += 1

Note that there are quite a few places you could optimize the code, but I am just going to leave the answer here, and let you figure other things out yourself.

Pokechu22 · Accepted Answer · 2014-11-22 00:37:54Z

0

Perhaps copying your code into this site went wrong, but regardless the code is not correctly formatted here which makes it very difficult to read.

regardless, its clear that you are indexing into a list to a point that doesn't exist. to help track down this error, add this line after you start your while loop:

print 'n %s, times %s, user_answers %s, answer_list %s' % (n, times, user_answers, answer_list)

then run the program and paste the output of the program into your question (but first please correct the indenting)

edited Nov 22, 2014 at 0:37

Pokechu22

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answered Oct 23, 2014 at 20:15

garyboland

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1 Comment

Jonty Morris Over a year ago

sorry about my code formatting. I'm very new to this site and probably should read the instructions more carefully because I'm not sure what is wrong with the format that my code is in

Jonty Morris · Accepted Answer · 2017-02-25 03:57:07Z

0

Due to an unknown reason, the testAnswers and userAnswers weren't in equal length. The lesson here is to always make sure they are the same length.

A simple if-statment can prevent the entire error.

if len(answers) != len(userAnswers):
    return

answered Feb 25, 2017 at 3:57

Jonty Morris

8172 gold badges12 silver badges26 bronze badges

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