Is there a way to not convert a variable to a different type if it can't be converted?

Question

For example :

    numberOneString = input("Input a number")
    
    numberOne = int(numberOne)
    
    print(numberOneString)

This gives an error when you try to run it if the input is a string that is not a number. Is there a way to stop that code from running if the variable cannot be converted to an int but run the code if it can be converted into an int?

You might also find https://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response useful. — Thierry Lathuille, Sep 01 '22 at 16:04

score 1 · Accepted Answer · answered Sep 01 '22 at 16:02

Python tends to take the view that you should ask forgiveness, not permission. With that in mind, the error thrown is a ValueError, so the idiomatic thing to do is to attempt the conversion and handle the case where it fails.

numberOneString = input("Input a number")
try:
    numberOne = int(numberOneString)
except ValueError:
    print("That's not a real number, please try again.")
    exit(1)
print(numberOne)

John Gordon · Answer 2 · 2022-09-01T16:11:04.457

0

Put the conversion inside a try/except block.

numberOne = input("Input a number")
# at this point, numberOne is a string

try:
    numberOne = int(numberOne)
    # if we get to this line, int succeeded, so numberOne is now an integer
except ValueError:
    pass

print(numberOne)
# at this point, numberOne may be an integer or a string

edited Sep 01 '22 at 16:11

answered Sep 01 '22 at 16:01

John Gordon

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Is there a way to not convert a variable to a different type if it can't be converted?

2 Answers2