Command line tool for toggling hosts file records

hostmod.py

#/usr/bin/env python
# hostmod.py -- Command line tool for toggling hosts file records
#
# Written in 2020 by W. Scott Means (smeans@gmail.com)
# To the extent possible under law, the author has dedicated all copyright
# and related and neighboring rights to this software to the public domain
# worldwide. This software is distributed without any warranty.
#
# You should have received a copy of the CC0 Public Domain Dedication along with
# this software. If not, see <https://creativecommons.org/publicdomain/zero/1.0/>.
import sys
import re
import argparse

hostpaths = {'win32': '/windows/system32/drivers/etc/hosts', 'linux': '/etc/hosts'}
line_endings = {'win32': '\n', 'linux': '\n'}

parser = argparse.ArgumentParser(description='toggles specified hostname in system hosts file')
parser.add_argument('switch', help='action to take', choices=['on', 'off', 'toggle', 'list'])
parser.add_argument('host', help='host name to switch', nargs='?')
parser.add_argument('-p', '--path', default=hostpaths[sys.platform])
parser.add_argument('-u', '--update', help='update hosts file in place', action='store_true')
parser.add_argument('-v', '--verbose', help='verbose output', action='store_true')
args = parser.parse_args()

sle = line_endings[sys.platform]

with open(args.path, 'r') as f:
  oldfile = f.read()

if args.switch == 'list':
    print(oldfile)
    sys.exit(0)

lines = oldfile.split(sle)

res = re.compile(r'(\s+)')

newfile = ''
found = False

nla = []
for line in lines:
    la = res.split(line.strip())

    if len(la) > 2 and la[2] == args.host:
        found = True
        shouldComment = la[0][0] != '#' if args.switch == 'toggle' else args.switch != 'on'

        if shouldComment:
            if la[0][0] != '#':
                la[0] = '#' + la[0]
        elif la[0][0] == '#':
            la[0] = la[0][1:]

    nla.append(''.join(la))

newfile = sle.join(nla)

if not found:
    print('hostmod: host %s not found' % args.host)

if newfile == oldfile:
    print('hostmod: no changes made', file=sys.stderr)
elif args.update:
    with open(args.path, 'w') as f:
        f.write(newfile)

if not args.update or args.verbose:
    print(newfile)