docstr: Gets called at the beginning of each epoch
docstr_tok: ["Gets","called","at","the","beginning","of","each","epoch"]
code: def on_stage_start(self, stage, epoch):
      """Gets called at the beginning of each epoch"""
      if stage != sb.Stage.TRAIN:
          self.bleu_4_metric = self.hparams.bleu_4_computer()
          self.bleu_2_metric = self.hparams.bleu_2_computer()
          self.hyps = []
          self.references = []
  
file_path: speechbrain/recipes/MultiWOZ/response_generation/llama2/train_with_llama2.py
imports: import sys
  import speechbrain
  import torch
  from itertools import chain
  from hyperpyyaml import load_hyperpyyaml
  from speechbrain.utils.distributed import run_on_main
  import math
  from speechbrain.dataio.batch import PaddedBatch
label_desc: Use image node_id 4 for calling the ResGenBrain obj's underlying member method code with example usage: obj.on_stage_start(stage, epoch) without return types