Only allowing Integer input in python 3.3.2

Hi i am trying to make the program only accept the numbers 0, 4, 6, and 12, and not allow anything else to be inputted. So far i have been successful in only allowing certain integers to be entered, however i am having trouble with not allowing any letters to be entered. When a letter is entered, the entire program crashes. Please could you help me only allow integers to be entered? Thank you.

My code is below:

from random import randint 
def simul():
    dice = int(input("What sided dice would you like to roll? 4, 6 or 12? 0 to not roll:"))
    if dice != 4 and dice!=6 and dice!=12 and dice!=0:
        print('You must either enter 4, 6, or 12')
        simul()
    elif dice==0:
        exit()
    else:
        while dice !=0 and dice==4 or dice==6 or dice ==12 :
            print (randint(1,dice))
            dice = int(input("What sided dice would you like to roll? 4, 6 or 12? press 0 to stop."))
simul()

A couple of things you could look for in your code:

• using try/catch is the recommended way to test input for many reasons including knowing the exact cause of the error
• you can reduce some of your ifs and elses by thinking a little more about how they are nested
• having the function call itself and using a while loop isn't the best way, use one or the other
• in your case, you don't really need to allow only integer input, what you're looking for is to only allow a 0, 4, 6, or 12, which you do with the if statement

from random import randint
def simul():
    while True:
        try:
            dice = int(input("What sided dice would you like to" \
                    " roll? 4, 6 or 12? 0 to not roll: "))
            if dice not in (4, 6, 12, 0):
                raise ValueError()
            break  # valid value, exit the fail loop
         except ValueError:
            print("You must enter either 4, 6, 12, or 0")

    if dice == 0:
        return 0

    print(randint(1, dice))
    return dice

if __name__ == '__main__':
    while simul() != 0:
        pass