code: def _validate_single_port_string(port):
      
      if ' ' not in port or len(port.split(' ')) != 2:
          raise ValueError(
              "Port '{}' should have exactly one space in it".format(port)
          )
      (external, internal) = port.split(' ')
      try:
          external = int(external)
      except ValueError:
          raise ValueError(
              "Port '{}' external port isn't an int".format(port)
          )
      if ':' not in internal:
          raise ValueError(
              "Port '{}' local address should be 'IP:port'".format(port)
          )
      if not internal.startswith('unix:'):
          ip, localport = internal.split(':')
          if ip != 'localhost' and not _is_non_public_numeric_address(ip):
              raise ValueError(
                  "Port '{}' internal IP '{}' should be a local "
                  "address".format(port, ip)
              )
docs: Validate a single string specifying ports for Onion
      services. These look like: "80 127.0.0.1:4321"