def crime_validation(crime):
    """ Decide if crime input is valid.

        Parameters:
            crime(str): A user's input to the crime level.

        Return:
            (str): A single valid string, such as "1", "2" or "3".
    """
    while crime != "1" and crime != "2" and crime != "3" :
        print("\nI'm sorry, but " + crime + " is not a valid choice. Please try again.")
        crime = input("\nHow much crime is acceptable when you travel?"
              + "\n  1) Low"
              + "\n  2) Average"
              + "\n  3) High"
              + "\n> ")
    return crime