code: def connect_partial_nodirect(self, config):
          
          assert 0 <= config.connection_fraction <= 1
          all_connections = self.compute_full_connections(config, False)
          shuffle(all_connections)
          num_to_add = int(round(len(all_connections) * config.connection_fraction))
          for input_id, output_id in all_connections[:num_to_add]:
              connection = self.create_connection(config, input_id, output_id)
              self.connections[connection.key] = connection
docs: Create a partially-connected genome,
          with (unless no hidden nodes) no direct input-output connections.