message: Tracking: Work around a Python version + wrapt property access issue
  I think we ran into a similar issue with different Python versions before. To be clear, I'm guessing that this will fix the nightly builds but have not verified.
diff: @@ -1001,6 +1001,17 @@ class _TupleWrapper(TrackableDataStructure, wrapt.ObjectProxy):
  .format(self.__wrapped__, self.__wrapped__._fields))
  return super(_TupleWrapper, self)._checkpoint_dependencies
  + def __getattribute__(self, name):
  + if (hasattr(type(self), name)
  + and isinstance(getattr(type(self), name), property)):
  + # Bypass ObjectProxy for properties. Whether this workaround is necessary
  + # appears to depend on the Python version but not the wrapt version: 3.4
  + # in particular seems to look up properties on the wrapped object instead
  + # of the wrapper without this logic.
  + return object.__getattribute__(self, name)
  + else:
  + return super(_TupleWrapper, self).__getattribute__(name)
  +
  def _is_function(x):
  return isinstance(x, (def_function.Function, defun.ConcreteFunction))
  