How to create a validation loop for multiple inputs

Question

I wrote some code to get 3 integers from the user. The code then prints the sum of the 3 integers. The code works as expected. I want to validate all input before doing the calculation. However, the code just doesn't feel right. Is there another approach I should be taking? It seems.. redundant. I am looking into nested try/except, but so far no luck.

msg = "Invalid Input"


while True:
    try:
        a = int(input("Enter 1st number: "))
        break
    except:
        print(msg)
while True:
    try:
        b = int(input("Enter 2nd number: "))
        break
    except:
        print(msg)
while True:
    try:
        c = int(input("Enter 3rd number: "))
        break
    except:
        print(msg)

print(a + b + c)

You could create a function and include on it the while loop and if needed a numerical range (interval) to validate the input so that your code be more cleaner. — sɪʒɪhɪŋ βɪstɦa kxɐll
– sɪʒɪhɪŋ βɪstɦa kxɐll, Commented Aug 28, 2020 at 21:21
@MiguelAvila thanks for the suggestion. I made some edits above. Is that what you were talking about? — okkv1747vm
– okkv1747vm, Commented Aug 28, 2020 at 22:55
Yes, I was referring to that. Btw this video youtube.com/watch?v=C-gEQdGVXbk&t=1781s is really useful, the dude mentions pretty efficient python features to be more expressive with less code. (I would recommend his channel) — sɪʒɪhɪŋ βɪstɦa kxɐll
– sɪʒɪhɪŋ βɪstɦa kxɐll, Commented Aug 29, 2020 at 1:49
Please do not update the code in your question after receiving answers, doing so goes against the Question + Answer style of Code Review. This is not a forum where you should keep the most updated version in your question. Please see what you may and may not do after receiving answers. — Mast
– Mast ♦, Commented Aug 29, 2020 at 6:50

FMc · Accepted Answer · 2020-08-28 23:12:03Z

Your revised code in on the right track. You can simplify the function a fair bit:

def get_integer_input(prompt):
    while True:
        try:
            # Just return directly. No need for an invalid_input flag.
            return int(input(prompt))
        except ValueError:
            print('Invalid input')

# Where you see repetition in your code, consider using a data structure to
# address it. There are libraries that will give you the ordinals. Personally,
# I would just rephrase the input() prompt so that the ordinals are not needed.
ORDINALS = ('1st', '2nd', '3rd')

# Get the integers.
fmt = 'Enter {} number: '
a, b, c = [get_integer_input(fmt.format(o)) for o in ORDINALS]
print(a + b + c)

# Or if you care only about the total, just get it directly.
tot = sum(get_integer_input(fmt.format(o)) for o in ORDINALS)
print(tot)

l0b0 · Accepted Answer · 2020-08-28 21:32:12Z

When you have three intimately related variables like this it would be natural to see whether this can be done as a list instead. Some tips to do that:

You can use a loop to collect all the items you want.
range(N) gives you a generator to iterate over numbers 0 through N.
You can either initialize an empty list inside the loop to avoid keeping old results, or continue from the last successfully gathered index to avoid asking the same question twice.
You can use the inflect library to generate ordinals.

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