How to take Integer user input in Python

Collecting integer input from users is a common requirement in interactive Python applications.

This guide explores various methods for obtaining integer input, including input validation, error handling, and range checking, allowing you to ensure your programs receive valid integer values.

Basic Integer Input with int()

The most basic approach to take integer input is by using the input() function to get a string from the user, and then immediately converting that string into an integer using the int() constructor:

user_input = int(input('Enter an integer: '))
print(user_input)

The input() function always returns a string. The int() constructor then attempts to convert the returned string to an integer.

Handling ValueError Exceptions

If the user enters a non-numeric string that can not be converted to an integer, the int() constructor raises a ValueError. Use a try/except block to handle this situation:

try:
    user_input = int(input('Enter an integer: '))
    print(user_input)
except ValueError:
    print('Enter a valid integer')

• The try block contains the code which can potentially throw an exception.
• The except ValueError block handles the ValueError exception, if the user types non numeric characters.

Validating Input with a Loop

To ensure that the user only enters a valid integer, embed the try/except block in a while loop:

while True:
    try:
        num = int(input('Your favorite integer: '))
        print(num)
        break
    except ValueError:
        print('Please enter an integer.')

Explanation:

• The while True loop continues to ask for input until a valid integer is entered.
• If int(input()) throws a ValueError, the except block is executed, an error message is printed and the loop continues with the continue statement.
• If the conversion is successful, the integer is printed and the loop is terminated using break.

Limiting Input to a Specific Range

You can add a range check using an if statement inside the try block, or you can raise your own ValueError when the number is out of range:

while True:
    try:
        num = int(input('Integer between 1 and 100: '))
        print(num)
        if not 1 <= num <= 100:
            raise ValueError
            break
    except ValueError:
        print('Please enter an integer between 1 and 100.')

Explanation:

• The while loop will continue to prompt the user for input until the user enters a valid integer within range.
• If the int(input()) throws a ValueError or the if condition is met, the except block is executed, an error message is printed and the loop continues.
• If the input is valid, the integer is printed and the loop breaks using the break keyword.