def board_fen_to_array(b):
    """
    The board FEN str parameter b is copied into a new string a.  
    Within the new string, each FEN integer indicator of empty squares
    is replaced by a corresponding number of spaces.  The modified FEN
    string is then split on '/' to produce an array or rank strings.
    For example, the board FEN excerpt '3P4/k1K5' would be transformed
    into the array ['   P    ', 'k K     '].  
    """
    a = str(b)
    for i in range(1, 9):
        a = a.replace(str(i), i*' ')
    return a.split('/')