Python Regular Expression parameter issue

Question

I'm currently creating a quiz to test children's ability to add, subtract and multiply two numbers together. You can see the code below as to what I have developed so far:

from random import randint
import re

first_number = randint(30,60)
second_number = randint(30,60)
correct_ans = str(first_number - second_number)

while True:
    user_input = input("%s - %s = " %(first_number, second_number))
    if re.search(r'[\d]', user_input):
        print("Error. You have entered a non - integer character. The question will be asked again.")
    elif re.search(r'[0-9]', user_input):
        if (user_input == correct_ans):
            print("Correct! Well done!")
            break
        else:
            print("Your answer is incorrect. The correct answer was %s" %(correct_ans))
            break

To explain the program briefly -
There are two random numbers generated, and this function ONLY multiplies the numbers together. A while loop asks the user for the correct result. Now, the first regular expression analyses the input to see if they have entered any non - digit characters (punctuation, letters) etc. If they have, they receive a message and the question is asked again.

Now, the second part of the if statement then checks to see that if they have entered a number, and if they have, then the program checks to see if the input is correct to the correct_ans. If it is, they receive a message saying well done! and the program breaks. If they get it wrong, the program outputs a message and they still get it wrong.

The issue that I'm having is that the IDLE is outputting the first message "Error, you have entered..." all the time, like this:

50 - 60 = -10
Error. You have entered a non - integer character. The question will be asked again.
50 - 60 =

How can I solve this? And more importantly, how can I get the computer to accept negative values for the subtraction operation, since it has a '-' and considers it a punctuation?

Hint: '10'.isdigit() and abs(-10)

Burhan Khalid
– Burhan Khalid

2014-12-22 11:11:01 +00:00
Commented Dec 22, 2014 at 11:11 — Burhan Khalid
– Burhan Khalid, Commented Dec 22, 2014 at 11:11

Padraic Cunningham · Accepted Answer · 2014-12-22 11:14:28Z

1

Just use a try/except which will handle negative numbers also:

from random import randint


first_number = randint(30,60)
second_number = randint(30,60)
correct_ans = first_number - second_number

while True:
    user_input = input("%s - %s = " %(first_number, second_number))
    try:
        user_input = int(user_input)
    except ValueError:
        print("Error. You have entered a non - integer character. The question will be asked again.")        
    else:
        if user_input == correct_ans:
            print("Correct! Well done!")
            break
        else:
            print("Your answer is incorrect. The correct answer was %s" %(correct_ans))
            break

answered Dec 22, 2014 at 11:14

Padraic Cunningham

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Comments

jaynp · Accepted Answer · 2014-12-22 11:13:29Z

1

I believe your regular expression is only looking for ONE digit. You should look into using repetition with your regex.

However, since you are looking for integer values, I think an easier way to do this would be to use Python's int function.

user_input = input("%s - %s = " %(first_number, second_number))
try:
    user_input = int(user_input)
except ValueError e:
    print("Error. You have entered a non - integer character. The question will be asked again.")

int accepts strings integer strings (including plus and minus signs, and ignoring whitespace) and is a much more robust way to validate integer input.

answered Dec 22, 2014 at 11:13

jaynp

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Comments

Daniel Roseman · Accepted Answer · 2014-12-22 11:15:22Z

0

I'm not quite sure what you think the first regex is doing. In fact, it is doing exactly the same thing as the second one, since [\d] is the same as [0-9].

You could use [^\d-] instead, to check that what you have is not a digit or the - character, but what you actually want is to check whether the value is a valid integer, which you can do by using the int function directly and catching the exception, as others have pointed out.

answered Dec 22, 2014 at 11:15

Daniel Roseman

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