def _hamming_distance(str1: str, str2: str) ->int:
    """
    Count the # of differences between strings str1 and str2,
    padding the shorter one with whitespace
    """
    diffs = 0
    if len(str1) < len(str2):
        str1, str2 = str2, str1
    len_dist = len(str1) - len(str2)
    str2 += ' ' * len_dist
    for ch1, ch2 in zip(str1, str2):
        if ch1 != ch2:
            diffs += 1
    return diffs
