def append(args):
    """
    %prog append csvfile [tag]

    Append a column with fixed value. If tag is missing then just append the
    filename.
    """
    p = OptionParser(append.__doc__)
    p.set_sep()
    p.set_outfile()
    opts, args = p.parse_args(args)

    nargs = len(args)
    if nargs not in (1, 2):
        sys.exit(not p.print_help())

    csvfile = args[0]
    tag = args[1] if nargs == 2 else csvfile
    fp = must_open(csvfile)
    fw = must_open(opts.outfile, "w")
    for row in fp:
        row = row.rstrip("\r\n")
        row = opts.sep.join((row, tag))
        print(row, file=fw)