sort command like elisp function sort-regexp-fields

sort-regexp-fields.py

# -*- coding: utf-8 -*-
#
# cat <<'EOD' | python sort-regexp-fields.py '[^;]+'
# using System;
# using System.Collections.Generic;
# using System.Web;
# using System.Web.UI;
# using System.Web.UI.WebControls;
# using System.Web.UI.HtmlControls;
# using System.Linq;
# EOD

import re
import sys
import getopt

def error(s):
    sys.stderr.write(s)
    sys.stderr.write('\n')
    sys.exit(1)

def usage():
    error('usage: %s [-r] key-extract-regex' % sys.argv[0])

def key(pattern, line):
    m = pattern.search(line)
    if m is None:
        return line
    elif m.groups():
        return m.group(1)
    else:
        return m.group(0)

try:
    opts, args = getopt.getopt(sys.argv[1:], 'r')
    opts = dict([(k[1:], v) for k, v in opts])
except getopt.GetoptError:
    usage()
if 1 <> len(args):
    usage()

try:
    pattern = re.compile(args[0])
    sys.stdout.writelines(sorted(sys.stdin.readlines(), key=lambda line: key(pattern, line), reverse='r' in opts))
except re.error:
    error('bad regex')