docstr: Gets called at the end of a epoch.
docstr_tok: ["Gets","called","at","the","end","of","a","epoch","."]
code: def on_stage_end(self, stage, stage_loss, epoch):
      """Gets called at the end of a epoch."""
      if stage == sb.Stage.TRAIN:
          self.train_loss = stage_loss
      else:
          per = self.per_metrics.summarize("error_rate")
  
      if stage == sb.Stage.VALID:
          old_lr, new_lr = self.hparams.lr_annealing(per)
          sb.nnet.schedulers.update_learning_rate(
              self.optimizer, new_lr
          )
  
          self.hparams.train_logger.log_stats(
              stats_meta={"epoch": epoch, "lr": old_lr},
              train_stats={"loss": self.train_loss},
              valid_stats={"loss": stage_loss, "PER": per},
          )
          self.checkpointer.save_and_keep_only(
              meta={"PER": per}, min_keys=["PER"]
          )
  
      if stage == sb.Stage.TEST:
          self.hparams.train_logger.log_stats(
              stats_meta={
                  "Epoch loaded": self.hparams.epoch_counter.current
              },
              test_stats={"loss": stage_loss, "PER": per},
          )
          run_on_main(
              save_metrics_to_file,
              args=[
                  self.hparams.test_wer_file,
                  self.transducer_metrics,
                  self.per_metrics,
              ],
          )
  
file_path: speechbrain/recipes/TIMIT/ASR/transducer/train.py
imports: import os
  import sys
  import logging
  import speechbrain
  from hyperpyyaml import load_hyperpyyaml
  from speechbrain.utils.distributed import run_on_main
label_desc: Use image node_id 4 for calling the ASR_Brain obj's underlying member method code with example usage: obj.on_stage_end(stage, stage_loss, epoch) without return types