code: def server_bind(self):
      
      socket_is_v6 = (
          hasattr(socket, 'AF_INET6') and self.socket.family == socket.AF_INET6)
      has_v6only_option = (
          hasattr(socket, 'IPPROTO_IPV6') and hasattr(socket, 'IPV6_V6ONLY'))
      if self._auto_wildcard and socket_is_v6 and has_v6only_option:
        try:
          self.socket.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
        except socket.error as e:
          # Log a warning on failure to dual-bind, except for EAFNOSUPPORT
          # since that's expected if IPv4 isn't supported at all (IPv6-only).
          if hasattr(errno, 'EAFNOSUPPORT') and e.errno != errno.EAFNOSUPPORT:
            logger.warn('Failed to dual-bind to IPv4 wildcard: %s', str(e))
      super(WerkzeugServer, self).server_bind()
docs: Override to enable IPV4 mapping for IPV6 sockets when desired.
  
      The main use case for this is so that when no host is specified, TensorBoard
      can listen on all interfaces for both IPv4 and IPv6 connections, rather than
      having to choose v4 or v6 and hope the browser didn't choose the other one.