BERT 打印loss

基于官方的https://github.com/google-research/bert

 if mode == tf.estimator.ModeKeys.TRAIN:

      train_op = optimization.create_optimizer(
          total_loss, learning_rate, num_train_steps, num_warmup_steps, use_tpu)

      logging_hook = tf.train.LoggingTensorHook({"loss": total_loss}, every_n_iter=10)

      output_spec = tf.contrib.tpu.TPUEstimatorSpec(
          mode=mode,
          loss=total_loss,
          train_op=train_op,
          training_hooks=[logging_hook],
          scaffold_fn=scaffold_fn)