class_docstr: Calculate BLEU for ST and MT models during training.
  
  :param y_hats: numpy array with predicted text
  :param y_pads: numpy array with true (target) text
  :param char_list: vocabulary list
  :param sym_space: space symbol
  :param sym_pad: pad symbol
  :param report_bleu: report BLUE score if True
docstr: Calculate corpus-level BLEU score in a mini-batch.
  
  :param torch.Tensor seqs_hat: prediction (batch, seqlen)
  :param torch.Tensor seqs_true: reference (batch, seqlen)
  :return: corpus-level BLEU score
  :rtype float
code: def calculate_corpus_bleu(self, ys_hat, ys_pad):
      """Calculate corpus-level BLEU score in a mini-batch.
  
      :param torch.Tensor seqs_hat: prediction (batch, seqlen)
      :param torch.Tensor seqs_true: reference (batch, seqlen)
      :return: corpus-level BLEU score
      :rtype float
      """
      seqs_hat, seqs_true = [], []
      for i, y_hat in enumerate(ys_hat):
          y_true = ys_pad[i]
          eos_true = np.where(y_true == -1)[0]
          ymax = eos_true[0] if len(eos_true) > 0 else len(y_true)
          # NOTE: padding index (-1) in y_true is used to pad y_hat
          # because y_hats is not padded with -1
          seq_hat = [self.char_list[int(idx)] for idx in y_hat[:ymax]]
          seq_true = [
              self.char_list[int(idx)]
              for idx in y_true
              if int(idx) != -1
          ]
          seq_hat_text = "".join(seq_hat).replace(self.space, " ")
          seq_hat_text = seq_hat_text.replace(self.pad, "")
          seq_true_text = "".join(seq_true).replace(self.space, " ")
          seqs_hat.append(seq_hat_text)
          seqs_true.append(seq_true_text)
      bleu = nltk.bleu_score.corpus_bleu(
          [[ref] for ref in seqs_true], seqs_hat
      )
      return bleu * 100
  
file_path: espnet/espnet/nets/e2e_mt_common.py
imports: from itertools import groupby
  import nltk
  import numpy
label_desc: Use image node_id 3 for calling the ErrorCalculator obj's underlying member method code with example usage: obj.calculate_corpus_bleu(ys_hat, ys_pad) and returns: unknown