def _get_concat_op_info(self) -> List[List[str]]:
        """
        Return a list of lists of input/output names of concat ops.
        """
        intermediate_output_names_list = self.get_intermediate_output_names(
            lambda op: (op.spec.type == "concat")
        )
        all_operations = self.block_info.operations
        concat_op_info_list = []

        for concat_output_name in intermediate_output_names_list:
            # Get a list of input names (to "values") of current concat op.
            arguments = all_operations[concat_output_name].spec.inputs["values"].arguments
            argument_list = [val.name for val in arguments if val.name is not None]

            # Append the output name of current concat op.
            argument_list.append(concat_output_name)

            # Append a list of input/output names of current concat op.
            concat_op_info_list.append(argument_list)

        return concat_op_info_list

        Return a list of lists of input/output names of concat ops.
        
coremltools/optimize/coreml/experimental/_model_debugger.py