message: Fix `TPUMirroredVariable` with Python 3.
diff: @@ -984,6 +984,13 @@ class TPUMirroredVariable(MirroredVariable):
  else:
  self._handle_id = self._common_name
  + def __getattr__(self, name):
  + if _enclosing_tpu_context() is None:
  + return super(TPUMirroredVariable, self).__getattr__(name)
  + else:
  + raise AttributeError(
  + "'{}' not accessible within a TPU context.".format(name))
  +
  def get(self, device=None):
  if (_enclosing_tpu_context() is None) or (device is not None):
  return super(TPUMirroredVariable, self).get(device=device)
  