Collatz exercise from Automate the Boring Stuff

# collatz.py

import sys

def collatz(intVal):
    if intVal % 2 == 0:
        return intVal // 2
    else:
        return (3 * intVal) + 1

while True:
    print('Enter a number: ')
    try:
        myNum = int(input())

        while myNum != 1:
            myNum = collatz(myNum)
            print(myNum)
        sys.exit()

    except ValueError:
        print('No, I said a number!')

    except:
        raise