code: def preprocess_example(self, example, unused_mode, unused_hparams):
      example["new_field"] = tf.constant([42.42])
      return example
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import tempfile
  import numpy
  from six.moves import range
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import data_reader
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
  from tensorflow.compat.v1 import estimator
label_desc: Use image node_id 5 for calling the TestProblem obj's underlying member method code with example usage: obj.preprocess_example(example, unused_mode, unused_hparams) and returns: example