class_docstr: Updates the train_time variable.
  
  Optionally stops training if we've passed a time limit.
class_docstr_tok: ["Updates","the","train_time","variable",".","Optionally","stops","training","if","we","'ve","passed","a","time","limit","."]
code: def before_run(self, _):
      self._last_run_start_time = time.time()
      if self._last_run_duration is not None:
          return tf.train.SessionRunArgs(
              [self._train_time, self._increment_op],
              feed_dict={
                  self._increment_amount: self._last_run_duration
              },
          )
      else:
          return tf.train.SessionRunArgs([self._train_time])
  
imports: import os
  import time
  from absl import logging
  from magenta.models.gansynth.lib import networks
  import numpy
  import tensorflow.compat.v1
  import tensorflow_gan
label_desc: Use image node_id 2 for calling the TrainTimeHook obj's underlying member method code with example usage: obj.before_run(_) and returns: tf, tf