Python: Validating earlier in the code

Question

This is my code which is a quiz for children. What I need help on is, after the code asks the user for its class, it should validates whether the input is valid or not straight away instead of doing it in the end and displaying the message "Sorry, we can not save your data as the class you entered is not valid." I've tried moving the whole if, elif, and else statements to straight after:

users_class = int(input("Which class are you in? (1,2 or 3)"))

But that doesn't help. Any help will be appreciated :)

import time
import random
import math
import operator as op

def test():
    num1 = random.randint(1, 10)
    num2 = random.randint(1, num1)

    ops = {
        '+': op.add,  
        '-': op.sub,
        '*': op.mul,
        }

    keys = list(ops.keys()) 
    rand_key = random.choice(keys)  
    operation = ops[rand_key]  

    correct_result = operation(num1, num2)

    print ("What is {} {} {}?".format(num1, rand_key, num2))
    user_answer= int(input("Your answer: "))

    if user_answer != correct_result:
        print ("Incorrect. The right answer is {}".format(correct_result))
        return False
    else:
        print("Correct!")
        return True

username=input("What is your name?")

print ("Hi {}! Wellcome to the Arithmetic quiz...".format(username))

users_class = int(input("Which class are you in? (1,2 or 3)"))

input("Press Enter to Start...")
start = time.time()

correct_answers = 0
num_questions = 10

for i in range(num_questions):
    if test():
        correct_answers +=1

print("{}: You got {}/{} {} correct.".format(username, correct_answers,  num_questions,
'question' if (correct_answers==1) else 'questions'))

end = time.time()
etime = end - start
timeTaken = round(etime)

print ("You completed the quiz in {} seconds.".format(timeTaken))

if users_class == 1:
    with open("class1.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))

elif users_class == 2:
    with open("class2.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))

elif users_class == 3:
    with open("class3.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))
else:
print("Sorry, we can not save your data as the class you entered is not valid.")

By valid, do you mean 1, 2 or 3 or do you mean an integer? Also, what does(n't) happen when you move the if's to after the input? — ᔕᖺᘎᕊ, Jan 25 '15 at 18:19
It must be 1,2 or 3. And I get this error- "NameError: name 'correct_answers' is not defined" — Hasiba, Jan 25 '15 at 18:23
Then move the correct_answers and timeTaken just before the if's as well. — ᔕᖺᘎᕊ, Jan 25 '15 at 18:59
Ive tried that. But the questions are still asked. I want it to end if the person enters an invalid value — Hasiba, Jan 25 '15 at 19:07
But does the `Sorry, we can not save your data as the class you entered is not valid.` message come before the questions? — ᔕᖺᘎᕊ, Jan 25 '15 at 19:10

score 0 · Answer 1 · answered Jan 25 '15 at 19:15

0

You just need to add an extra condition following the question about which class the user is in. Normally we would have a loop here so that the user is asked again if they enter an invalid response.

print ("Hi {}! Welcome to the Arithmetic quiz...".format(username))
while True:
    users_class = int(input("Which class are you in? (1,2 or 3)"))
    if users_class in [1, 2, 3]:
        break
    print('Please make sure you enter a class from 1 to 3')

answered Jan 25 '15 at 19:15

Stuart

9,597
1
21
30

I get an error saying- NameError: name 'user_class' is not defined – Hasiba Jan 25 '15 at 22:08
It sounds like you typed `user_class` instead of `users_class` – Stuart Jan 26 '15 at 01:37

score 0 · Accepted Answer · answered Jan 25 '15 at 19:15

You should check that the input is valid immediately after the input, something like this:

import sys

users_class = int(input("Which class are you in? (1,2 or 3)"))

if users_class not in {1,2,3}:
    print("Sorry, you must enter either a 1, 2, or 3!")
    sys.exit(1)

Note that the sys.exit(1) call will exit the program.

Now, this isn't the most robust way to do things. If the user inputs something other than a number, for example, int(...) will raise an exception, because it can't convert, say, "dog", to an integer. Furthermore, you might prefer that the program continue asking for valid input, rather than just stopping and exiting. Here's some code that will do just that:

while True:
    try:
        # try to convert the user's input to an integer
        users_class = int(input("Which class are you in? (1,2 or 3)"))
    except ValueError:
        # oh no!, the user didn't give us something that could be converted
        # to an int!
        print("Please enter a number!")
    else:
        # Ok, we have an integer... is it 1, 2, or 3?
        if users_class not in {1,2,3}:
            print("Please enter a number in {1,2,3}!")
        else:
            # the input was 1,2, or 3! break out of the infinite while...
            break

print(users_class)

Thanks! works great. But last question. How do I only allow the user to enter an integers during the quiz? — Hasiba, Jan 25 '15 at 22:14
@Hasiba Same idea, just without the `if users_class not in ...` part. See [this answer](http://stackoverflow.com/a/23294659/1231929) for a detailed explanation. Since you'll be doing this multiple times throughout your program, it might be a good idea to make the input validating code into a function. That link gives an example of such. — jme, Jan 25 '15 at 22:45

score 0 · Answer 3 · answered Jan 25 '15 at 19:15

You need to check whether the value is 1, 2 or 3 straight after you ask them, so, you can move the if's directly after the users_class = int(input("Which class are you in? (1,2 or 3)")).

Move the correct_answers=0 above the if's and set timeTaken to 0 before.

This works:

import time
import random
import math
import operator as op
import sys

def test():
    num1 = random.randint(1, 10)
    num2 = random.randint(1, num1)

    ops = {
        '+': op.add,  
        '-': op.sub,
        '*': op.mul,
        }

    keys = list(ops.keys()) 
    rand_key = random.choice(keys)  
    operation = ops[rand_key]  

    correct_result = operation(num1, num2)

    print ("What is {} {} {}?".format(num1, rand_key, num2))
    user_answer= int(input("Your answer: "))

    if user_answer != correct_result:
        print ("Incorrect. The right answer is {}".format(correct_result))
        return False
    else:
        print("Correct!")
        return True

username=input("What is your name?")

print ("Hi {}! Wellcome to the Arithmetic quiz...".format(username))

users_class = int(input("Which class are you in? (1,2 or 3)"))

correct_answers = 0
timeTaken = 0

if users_class == 1:
    with open("class1.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))

elif users_class == 2:
    with open("class2.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))

elif users_class == 3:
    with open("class3.txt","a+") as f:
        f.write("   {}:Scored {} in {} seconds.".format(username,correct_answers,timeTaken))
else:
    print("Sorry, we can not save your data as the class you entered is not valid.")
    sys.exit(0);

input("Press Enter to Start...")
start = time.time()

num_questions = 10

for i in range(num_questions):
    if test():
        correct_answers +=1

print("{}: You got {}/{} {} correct.".format(username, correct_answers,  num_questions,
'question' if (correct_answers==1) else 'questions'))

end = time.time()
etime = end - start
timeTaken = round(etime)

print ("You completed the quiz in {} seconds.".format(timeTaken))

If it's invalid, then quit via sys, otherwise continue as your current code does.

Working [here](http://www.tutorialspoint.com/execute_python3_online.php?PID=0Bw_CjBb95KQMcjZxX0EtZHIzRUk) — ᔕᖺᘎᕊ, Jan 25 '15 at 19:20

Python: Validating earlier in the code

3 Answers3