docs: def select_address_family(host, port):
      """Return ``AF_INET4``, ``AF_INET6``, or ``AF_UNIX`` depending on
      the host and port."""
      # disabled due to problems with current ipv6 implementations
      # and various operating systems.  Probably this code also is
      # not supposed to work, but I can't come up with any other
      # ways to implement this.
      # try:
      #     info = socket.getaddrinfo(host, port, socket.AF_UNSPEC,
      #                               socket.SOCK_STREAM, 0,
      #                               socket.AI_PASSIVE)
      #     if info:
      #         return info[0][0]
      # except socket.gaierror:
      #     pass
      if host.startswith("unix://"):
          return socket.AF_UNIX
      elif ":" in host and hasattr(socket, "AF_INET6"):
          return socket.AF_INET6
      return socket.AF_INET