import re


def slice_marc_shorthand(string: str) -> tuple:
    """
    Splits a string and gives a tuple of two elements containing the Main Number and the subfield of a marc shorthand
    Calls a regex check to make sure the format is corret
    :param str string: a string describing a marc shorthand, should look like this '504:a', second part can also be a number or 'i1', 'i2' and 'none'
    :return: either (None, False) or (field, subfield)
    :rtype: tuple
    """
    match = re.match(r"^[0-9]{1,3}:\w*$", string)
    if match:
        a_list = string.split(":")
        return int(str(a_list[0]).lstrip("0")), a_list[1]
    else:
        return None, False