code: def guess_external_url(local_host, port):
      
      if local_host in ['0.0.0.0', '::']:
          # The server is listening on all interfaces, but we have to pick one.
          # The system's FQDN should give us a hint.
          local_host = socket.getfqdn()
  
          # https://github.com/vfaronov/turq/issues/9
          match = IPV4_REVERSE_DNS.match(local_host)
          if match:
              local_host = '.'.join(reversed(match.groups()))
          else:
              match = IPV6_REVERSE_DNS.match(local_host)
              if match:
                  address_as_int = int(''.join(reversed(match.groups())), 16)
                  local_host = str(IPv6Address(address_as_int))
  
      if ':' in local_host:
          # Looks like an IPv6 literal. Has to be wrapped in brackets in a URL.
          # Also, an IPv6 address can have a zone ID tacked on the end,
          # like "%3". RFC 6874 allows encoding them in URLs as well,
          # but in my experiments on Windows 8.1, I had more success
          # removing the zone ID altogether. After all this is just a guess.
          local_host = '[%s]' % local_host.rsplit('%', 1)[0]
  
      return 'http://%s:%d/' % (local_host, port)
docs: Return a URL that is most likely to route to `local_host` from outside.
  
      The point is that we may be running on a remote host from the user's
      point of view, so they can't access `local_host` from a Web browser just
      by typing ``http://localhost:12345/``.