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.acc_metric = []
  
imports: import logging
  import sys
  import time
  from functools import partial
  import speechbrain
  import torch
  import torch.nn.functional
  from torch.nn.parallel import DistributedDataParallel
  from hyperpyyaml import load_hyperpyyaml
  from speechbrain import Stage
  from speechbrain.utils.distributed import run_on_main
  from speechbrain.dataio.dataloader import SaveableDataLoader
  from speechbrain.dataio.sampler import DynamicBatchSampler
  from speechbrain.lobes.models.wav2vec import w2v_mask_collate_fn
  from speechbrain.lobes.models.wav2vec import sample_negatives
  from speechbrain.core import AMPConfig
label_desc: Use image node_id 6 for calling the W2V2Brain obj's underlying member method code with example usage: obj.on_stage_start(stage, epoch) without return types