code: def before_run(self, run_context):
      if self.global_step_tensor is not None:
          requests = {"global_step": self.global_step_tensor}
          return tf.estimator.SessionRunArgs(requests)
      else:
          return None
  
imports: import itertools
  import numpy
  import tensorflow
  from tensorflow_estimator.python.estimator.export.export import build_supervised_input_receiver_fn_from_input_fn
label_desc: Use image node_id 3 for calling the _TrainLogHook obj's underlying member method code with example usage: obj.before_run(run_context) and returns: tf, None