def ham_dist(one: str, two: str) -> int:
    """Calculates HAMming DISTance between two strings

    'Hamming distance' is the number of substituted chars

    :param one: a string
    :type one: str
    :param two: a string to compare to one
    :type two: str
    :returns: the substitution distance between one and two
    :rtype: int
    """
    
    if not one or not two:
        raise ValueError('Cannot find distance between empty strings')
    if len(one) != len(two):
        raise ValueError('Strings must be of the same length')
    dist = 0
    for i in range(len(one)):
        if one[i] != two[i]:
            dist += 1
    return dist