message: Fix sort dict keys for python3.
diff: @@ -1133,7 +1133,7 @@ def _get_correct_mapping(original_index, nodes):
  # If it is -1, return the last index.
  if original_index == -1:
  node_indices = nodes.keys()
  - node_indices.sort()
  + node_indices = sorted(node_indices)
  return node_indices[-1]
  else:
  return original_index
  