code: def compute_update(self, x, y):
      # TODO(rkn): Computing the weights before and after the training step
      # and taking the diff is awful.
      weights = self.get_weights()[1]
      self.sess.run(
          self.train_step,
          feed_dict={self.x: x, self.y_: y, self.keep_prob: 0.5},
      )
      new_weights = self.get_weights()[1]
      return [x - y for x, y in zip(new_weights, weights)]
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import time
  import tensorflow
  from tensorflow.examples.tutorials.mnist import input_data
  import ray
  import ray.experimental.tf_utils
  from bigdl.dllib.utils.log4Error import invalidInputError
label_desc: Use image node_id 2 for calling the SimpleCNN obj's underlying member method code with example usage: obj.compute_update(x, y) and returns: unknown