return a string indicating the type of special node represented by
    the stat buffer st (block, character, fifo, socket).

def _node_type(st):
    """ return a string indicating the type of special node represented by
    the stat buffer st (block, character, fifo, socket).
    """
    _types = [
        (stat.S_ISBLK, "block device"),
        (stat.S_ISCHR, "character device"),
        (stat.S_ISFIFO, "named pipe"),
        (stat.S_ISSOCK, "socket")
    ]
    for t in _types:
        if t[0](st.st_mode):
            return t[1]