I think we need to keep these functions and raise NotImplementedError, because by removing we would inherit the functionality from Axes, which does not work for 3D.

Ok. The python docs state that NotImplementedError should not be used to indicate that an operator or method is not meant to be supported at all, but rather if the method is still being developed etc. Do you still want to go ahead with it? Do you have any more plans for this, like getting rid of the frame_on concept entirely?

From the note in the docs, it looks like the recommended approach is to set the method to None.
https://docs.python.org/3/library/exceptions.html#NotImplementedError

Setting to none (plus leaving a comment there) seems the right approach. Thanks for checking the meaning of NotImplementedError.

My understanding of the guidance is to set the actual method to None, rather than the return value. I couldn’t find any examples by googling, but here is one I happen to know about in another project, where we wanted to disable the __iter__ method.

https://github.com/SciTools/iris/blob/c74d78331aeb394383d1552e3d1679b0f734b402/lib/iris/cube.py#L2551-L2553

Sorry for not seeing this until now. Good that things were clarified in the meanwhile. I think a note in doc/api/next_api_changes/removals/ would be nice. Basically saying that they were not working and therefore removed. If nothing else we can point at it, in case someone reports an error later. Other than that, is should be good to go!