    def size(self, index):
        """Return an example's size as a float or tuple. This value is used when
        filtering a dataset with ``--max-positions``."""
        if len(self.sizes) == 1:
            return self.sizes[0][index]
        else:
            return (s[index] for s in self.sizes)
Return an example's size as a float or tuple. This value is used when
filtering a dataset with ``--max-positions``.
fairseq/data/nested_dictionary_dataset.py