def three_dig_format(digit):
    """
    Create string of 3 digits given any digit < 1000
    """
    if digit.isdigit() and len(digit) < 4:
        if len(digit) == 3:
            return digit
        elif len(digit) == 2:
            return "0" + digit
        elif len(digit) == 1:
            return "00" + digit