Python : verifying user's input?

Question

My variable userAnswerList[] takes the user's input, and I need to verify if the user has input other than A, B, C, D.

Here's my code below, and wondering how should I validate user's input between the range of (A B C D) and if not print the error message?

answerList = ["A","C","A","A","D","B","C","A","C","B","A","D","C","A","D","C","B","B","D","A"]
userAnswerList = []
correct = 0
incorrect = 0

def main():
    for i in range(20):
        i = i + 1
        answer = input("Please Enter the answer for Question %d:" %i)
        userAnswerList.append(answer)
        numCorrect = [i for i in userAnswerList if i in answerList]

    if len(numCorrect) > 15:
        print("Congratulations You have passed the exam!")
    elif len(numCorrect) < 15:
        print("Failed....Please try again")

correct = len(numCorrect)
incorrect = 20 - correct

print("Correct Answers:",correct,"/ Incorrect Answers:",incorrect)  

main()

If your next question is going to be "ok, I figured out how to check if a variable is A B C or D. Now how do I go back and ask the user to try again?", this may be useful to you: [Asking the user for input until they give a valid response](http://stackoverflow.com/q/23294658/953482) — Kevin, Apr 14 '15 at 17:04

Matt Davidson · Accepted Answer · 2015-04-14T17:46:49.317

3

You are already using the in syntax well. If you only want to check whether the answer is either A, B, C or D the following code would work.

if not answer in ['A', 'B', 'C', 'D']:
    print("Invalid answer.")

This script can further benefit from Python's syntax as such:

if answer not in 'ABCD':
    print("Invalid answer.")

edited Apr 14 '15 at 17:46

answered Apr 14 '15 at 17:02

Matt Davidson

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In Python it is more clear to do `answer not in [...]` than `not answer in [...]`. – Uyghur Lives Matter Apr 14 '15 at 17:03
1

If these are single-letter answers, you can even use `'ABCD'` instead of `['A', 'B', 'C', 'D']`. – Arkanosis Apr 14 '15 at 17:04
yes, there are single-letter answers.. so should I try [ABCD] ? – kyle lee Apr 14 '15 at 17:08
You can test for membership (whether the answer is in the object you are comparing to) via `'ABCD'` or `['A', 'B', 'C', 'D']`. The decision is purely style as they would give the same answer. – Matt Davidson Apr 14 '15 at 17:48

score -1 · Answer 2 · edited Jul 25 '15 at 12:37

-1

import re

if re.match("^[ABCDabcd]$", answer) is not None:
    # Matched!
else:
    # Didn't match!

edited Jul 25 '15 at 12:37

Falko

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answered Apr 14 '15 at 17:02

Carson Crane

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regex seems like overkill here. You can solve the problem using only built-in functionality. – Kevin Apr 14 '15 at 17:03

Python : verifying user's input?

2 Answers2