code: def _nested_op(inputs, op):  # pylint: disable=invalid-name
    
    # First the simple non-nested case.
    if not isinstance(inputs[0], (list, tuple)):
      return op(inputs)
    # In the nested case, sum on each axis separately.
    result_list = []
    for i in range(len(inputs[0])):
      result_list.append(_nested_op([x[i] for x in inputs], op=op))
    if isinstance(inputs[0], list):
      return result_list
    return tuple(result_list)
docs: Helper: sum a list of arrays or nested arrays.