From Terry's comment on PR11472 for issue 35689: 
> I don't like the use of class variables to initialize volatile instance state variables. I think it confuses the code a bit. Better, I think, to put them in an `init_state` method called from `__init__`. (I am not sure if method could be used in tests.) Since the tests do not access the class vars directly on the class, they should not be affected. I am leaving this minor refactoring for another issue after merging the tests. Then we can modify the class docstring.