def msg(num, txt=['plus', 'minus', 'zero', 'other']):
    """
    return message text for +1,-1, 0, other (e.g. None)
    """
    #
    if num == 1:
        str = txt[0]
    elif num == -1:
        str = txt[1]
    elif num == 0:
        str = txt[2]
    else:
        str = txt[3]
    return str