src/transformers/onnx/config.py/OnnxSeq2SeqConfigWithPast/outputs
class OnnxSeq2SeqConfigWithPast:    def outputs(self) -> Mapping[str, Mapping[int, str]]:
        common_outputs = super(OnnxConfigWithPast, self).outputs
        # Renaming the outputs axes properly.
        for name, axes_names in common_outputs.items():
            sequence_name = "encoder_sequence" if "encoder" in name else "decoder_sequence"
            for axis_idx, name in axes_names.items():
                if "sequence" in name:
                    axes_names[axis_idx] = sequence_name
                # We reset the value as the order in common_outputs (OrderedDict) is lost otherwise
                else:
                    axes_names[axis_idx] = name
        if self.use_past:
            self.fill_with_past_key_values_(common_outputs, direction="outputs")

        return common_outputs