    def __getitem__(self, index):
        """
        Returns a single sample from *tgt_dataset*. Note that backtranslation is
        not applied in this step; use :func:`collater` instead to backtranslate
        a batch of samples.
        """
        return self.tgt_dataset[index]
Returns a single sample from *tgt_dataset*. Note that backtranslation is
not applied in this step; use :func:`collater` instead to backtranslate
a batch of samples.
fairseq/data/backtranslation_dataset.py