Code improvements once Python 2 support is dropped

[jlstevens]

The idea of this issue is to remind ourselves of specific code improvements we can implement once we finally drop Python 2 support. Feel free to edit this comment and add new items.

• Replacement for cell magic with tab-completion #3173 : options(self, *args, backend=None, clone=True, **kwargs) (supported by Py3) is a nicer signature than options(self, *args, **kwargs) (required by Py2).