Hi folks, It's great to see the momentum building behind the project to migrate to Python 3. From the roadmap https://github.com/cctbx/cctbx_project/wiki/Python-3-roadmap, there is clearly still some way to go, but current activity makes me wonder if the proposed deadline of complete migration by 2020 might be beaten easily. What is not clear from the roadmap is whether there are any plans for a post-transition grace period, in which we have switched from writing forwards compatible Python 2 code to writing backwards compatible Python 3 code. Has this been thought about? Or will it be the case that the first commit of Py3-only code seals the deal? I ask because CCP4 has to support a large number of Python projects and these have not all considered the Python 3 switch nearly as seriously as cctbx yet. What I would like to request is a reasonable period of backwards compatibility is ensured to allow other CCP4 projects to catch up, and that this protected period is enshrined within the roadmap or developer guidelines. What do you think? Best wishes -- David