How could this code use the ValueError function

Question

if op == '+':
    left1 = random.randint(1,100)
    right1 = random.randint(1,100)
    print ("What is " + (str(left1) + op + str(right1) + "?"))
    answer  = eval(str(left1) + op + str(right1))
    guess = int(input(""))
    if guess == answer:
        print("Correct!")
        score + 1
    elif guess != answer:
        print("Incorrect")
    else:
        except ValueError:
            print("Expected integer")

I tried except ValueError, but it stated that it was invalid syntax. I'm trying to get the code to force the user to enter an integer for the answer, if they don't then it tells them that they are supposed to enter an integer.

You need to put your code (that you think may `ValueError` out) into a `try` block *before* the `except` block. — Ffisegydd, Mar 18 '15 at 16:17
https://docs.python.org/3/tutorial/errors.html#handling-exceptions — jonrsharpe, Mar 18 '15 at 16:18
@DanielJimenez: to create a valid Python expression in a string. It is redundant here because the code already determined that `op` is `+`, so you could just use `answer = left1 + right1`. — Martijn Pieters, Mar 18 '15 at 16:20
@DanielJimenez: inexperience on the part of the OP, presumably. — Martijn Pieters, Mar 18 '15 at 16:25

score 0 · Answer 1 · edited May 23 '17 at 12:22

ValueError is not a function; it is a class (an Exception subclass).

You need to use except as part of a try statement, it cannot be used on its own; you need to put any code you want 'protected' inside the try:

if op == '+':
    left1 = random.randint(1,100)
    right1 = random.randint(1,100)
    print ("What is " + (str(left1) + op + str(right1) + "?"))
    answer  = eval(str(left1) + op + str(right1))

    try:
        guess = int(input(""))
    except ValueError:
        print("Expected integer")
    else:    
        if guess == answer:
            print("Correct!")
            score = score + 1  # don't forget to *store* the sum!
        else:
            print("Incorrect")

You probably want to read the canonical Stack Overflow question on user input in Python to learn more about this: Asking the user for input until they give a valid response, as well as the section on handling exceptions in the Python tutorial.

How could this code use the ValueError function

1 Answers1