message: Silence a noisy __del__
  Popped up sometimes, looking something like:
  Exception ignored in: <bound method BaseSession.__del__ of <tensorflow.python.client.session.Session object at 0x7ff8f47827f0>>
  Traceback (most recent call last):
  File "[...]tensorflow/python/client/session.py", line 738, in __del__
  TypeError: 'NoneType' object is not callable
  Which I'm guessing is TF_DeleteSession being None.
diff: @@ -736,10 +736,11 @@ class BaseSession(SessionInterface):
  if self._session is not None:
  try:
  tf_session.TF_DeleteSession(self._session)
  - except AttributeError:
  - # At shutdown, `c_api_util` or `tf_session` may have been garbage
  - # collected, causing the above method calls to fail. In this case,
  - # silently leak since the program is about to terminate anyway.
  + except (AttributeError, TypeError):
  + # At shutdown, `c_api_util`, `tf_session`, or
  + # `tf_session.TF_DeleteSession` may have been garbage collected, causing
  + # the above method calls to fail. In this case, silently leak since the
  + # program is about to terminate anyway.
  pass
  self._session = None
  