message: Use a regular dictionary instead of an object-identity dictionary when printing node names (object-identity was left over from when regular objects were keys)
  Object-identity dictionaries and Python integers don't mix except for the few that get interned.
diff: @@ -89,7 +89,7 @@ class _ObjectGraphProtoPrettyPrinter(object):
  """Lazily creates a mapping from node id to ("path", "to", "root")."""
  if self._node_name_cache is not None:
  return self._node_name_cache
  - path_to_root = object_identity.ObjectIdentityDictionary()
  + path_to_root = {}
  path_to_root[0] = ("(root)",)
  to_visit = collections.deque([0])
  while to_visit:
  