code: def on_train_begin(self, unused_logs):
      _MockCallable.mock_call()
  
imports: import json
  import os
  import tempfile
  from unittest import mock
  from absl import flags
  import numpy
  import tensorflow
  from tensorflow_cloud.tuner import cloud_fit_client
  from tensorflow_cloud.tuner import cloud_fit_remote
  from tensorflow_cloud.tuner import cloud_fit_utils
label_desc: Use image node_id 1 for calling the CustomCallbackExample obj's underlying member method code with example usage: obj.on_train_begin(unused_logs) without return types