old_contents: #!/usr/bin/env python3
  # swap your /etc/resolv.conf depending on arguments
  # takes one argument, "localhost" or "system"
  # mod-resolveconf.py localhost (point everything to localhost)
  # mod-resolvconf.py system (revert everything to what DHCP or other sets)
  # this is useful for running pi-hole as a local container for your DNS
  # https://hobo.house/2018/02/27/block-advertising-with-pi-hole-and-raspberry-pi/
  
  import sys
  import shutil
  
  if len(sys.argv[1:]) != 1:
      print ("## Requires 1 argument ##")
      print ("mod-resolveconf.py localhost|system")
      exit(1)
  
  # backup /etc/resolv.conf then set it to 'localhost'
  def main():
      if sys.argv[1] == "localhost":
          shutil.copy2('/etc/resolv.conf', '/tmp/resolv.conf.system')
          dns = 'nameserver localhost\n'
          resolvconf = '/etc/resolv.conf'
          editconflocal = open(resolvconf, 'w')
          editconflocal.write(dns)
          editconflocal.close()
          print ("Updating /etc/resolv.conf to localhost...")
          print ("-----------------")
          with open(resolvconf, 'r') as result:
              shutil.copyfileobj(result, sys.stdout)
  
  # revert /etc/resolv.conf from backup if it exists
      if sys.argv[1] == "system":
          try:
              resolvconf = '/etc/resolv.conf'
              shutil.copy2('/tmp/resolv.conf.system', '/etc/resolv.conf')
              print ("Reverting %s back to /tmp/resolv.conf.system ..." % resolvconf)
              print ("-----------------")
              with open(resolvconf, 'r') as result:
                  shutil.copyfileobj(result, sys.stdout)
          except IOError:
              print ("No /tmp/resolv.conf.system found, may be running defaults")
  
  
  if __name__ == '__main__':
      main()
  
new_contents: #!/usr/bin/env python3
  # swap your /etc/resolv.conf depending on arguments
  # takes one argument, "localhost" or "system"
  # mod-resolveconf.py localhost (point everything to localhost)
  # mod-resolvconf.py system (revert everything to what DHCP or other sets)
  # this can useful for running pi-hole as a local container for your DNS
  # https://hobo.house/2018/02/27/block-advertising-with-pi-hole-and-raspberry-pi/
  
  import sys
  import shutil
  import subprocess
  
  if len(sys.argv[1:]) != 1:
      print ("## Requires 1 argument ##")
      print ("mod-resolveconf.py localhost|system")
      exit(1)
  
  # if you choose localhost, check DNS is working first
  if sys.argv[1] == "localhost":
      dns_command = 'dig @localhost hobo.house'
      try:
          subprocess.check_output(dns_command, shell=True, stderr=subprocess.STDOUT)
      except subprocess.CalledProcessError as e:
          ret = e.returncode
          if ret != 0:
              print("Cannot do DNS lookups against your localhost pi-hole, quitting.")
              exit(1)
  
  # backup /etc/resolv.conf then set it to 'localhost'
  def main():
      if sys.argv[1] == "localhost":
          shutil.copy2('/etc/resolv.conf', '/tmp/resolv.conf.system')
          dns = 'nameserver localhost\n'
          resolvconf = '/etc/resolv.conf'
          editconflocal = open(resolvconf, 'w')
          editconflocal.write(dns)
          editconflocal.close()
          print ("Updating /etc/resolv.conf to localhost...")
          print ("-----------------")
          with open(resolvconf, 'r') as result:
              shutil.copyfileobj(result, sys.stdout)
  
  # revert /etc/resolv.conf from backup if it exists
      if sys.argv[1] == "system":
          try:
              resolvconf = '/etc/resolv.conf'
              shutil.copy2('/tmp/resolv.conf.system', '/etc/resolv.conf')
              print ("Reverting %s back to /tmp/resolv.conf.system ..." % resolvconf)
              print ("-----------------")
              with open(resolvconf, 'r') as result:
                  shutil.copyfileobj(result, sys.stdout)
          except IOError:
              print ("No /tmp/resolv.conf.system found, may be running defaults")
  
  
  if __name__ == '__main__':
      main()
  
subject: add check that DNS is working first