A script to change DNS servers when using systemd-resolved

changedns.py

#!/usr/bin/env python3

from os import listdir
from pydbus import SystemBus
import socket

nics = listdir("/sys/class/net/")
nics.remove("lo")

for idx, nic in enumerate(nics):
    print(idx, nic)

nic_choice_input = input("Which NIC to apply to? ")

if nic_choice_input.isdigit():
    nic_choice = nics[int(nic_choice_input)]
else:
    nic_choice = nic_choice_input

dns_servers = [
    "1.0.0.1 1.1.1.1",
    "8.8.4.4 8.8.8.8",
    "8.8.4.4 1.0.0.1",
    "9.9.9.9 149.112.112.112",
    "208.67.222.222 208.67.220.220"
]

for idx, server in enumerate(dns_servers):
    print(idx, server)

servers_choice_input = input("Which server? ")

if servers_choice_input.isdigit():
    servers_choice = dns_servers[int(servers_choice_input)].split(" ")
else:
    servers_choice = servers_choice_input.split(" ")

# https://www.freedesktop.org/wiki/Software/systemd/resolved/
# https://wiki.freedesktop.org/www/Software/systemd/writing-network-configuration-managers/

system_bus = SystemBus()
resolve = system_bus.get("org.freedesktop.resolve1", "/org/freedesktop/resolve1")

with open("/sys/class/net/%s/ifindex" % nic_choice, "r") as f:
    ifindex = int(f.read())

servers = list(map(lambda ip: (socket.AF_INET, socket.inet_aton(ip)), servers_choice))
resolve.RevertLink(ifindex)  # to clear out previously configured servers
resolve.SetLinkDNS(ifindex, servers)

This is just like running # resolvectl dns INTERFACE SERVERS