Checking that input is an integer between 1 and 3 - Python

Question

I want to be able to check that an input is an integer between 1 and 3, so far I have the following code:

userChoice = 0

while userChoice < 1 or userChoice > 3:
    userChoice = int(input("Please choose a number between 1 and 3 > "))

This makes the user re-enter a number if it is not between 1 and 3, but I want to add validation to ensure that a user cannot enter a string or unusual character that may result in a value error.

Do add the [tag:python-3.x] tag if you are using python3 as `input` has been changed from 2 to 3 — Bhargav Rao, Mar 28 '15 at 17:33

vaultah · Accepted Answer · 2015-03-28T17:28:20.180

Catch the ValueError:

Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value

Example:

while userChoice < 1 or userChoice > 3:
    try:
        userChoice = int(input("Please choose a number between 1 and 3 > "))
    except ValueError:
        print('We expect you to enter a valid integer')

Actually, since the range of allowed numbers is small, you can operate directly on strings:

while True:
    num = input('Please choose a number between 1 and 3 > ')
    if num not in {'1', '2', '3'}:
        print('We expect you to enter a valid integer')
    else:
        num = int(num)
        break

score 1 · Answer 2 · answered Mar 28 '15 at 17:30

Alternatively try comparison of input in desired results, and break from the loop, something like this:

while True:
    # python 3 use input
    userChoice = raw_input("Please choose a number between 1 and 3 > ")
    if userChoice in ('1', '2', '3'):
        break
userChoice = int(userChoice)
print userChoice

Using Try/Except is a good approach, however your original design has a flaw, because user can still input like "1.8" which isn't exactly an integer but will pass your check.

Checking that input is an integer between 1 and 3 - Python

2 Answers2