code: def build_graph(self):
          
          self.global_step = tf.Variable(0, trainable=False)
          self._build_model()
          if self.mode == "train":
              self._build_train_op()
          else:
              # Additional initialization for the test network.
              self.variables = ray.experimental.tf_utils.TensorFlowVariables(
                  self.cost)
              self.summaries = tf.summary.merge_all()
docs: Build a whole graph for the model.