Hi David,

The plan is to have code that is compatible with both Python 2 and Python 3. In terms of a post-transition period, I don't think we've though about a timeline for when we make the switch to Python 3 only, so it's open for discussion. I'm trying to get things running on Python 3 first!

I don't know if a specific month in 2020 has been set yet for the official end of Python 2, so the period of Python 2/3 compatibility can probably go into 2020. And since Python 2.0 source code is still available, I would guess that Python 2.7 source code will be available for a while in case we need it past the official end of Python 2.

--
Billy K. Poon
Research Scientist, Molecular Biophysics and Integrated Bioimaging
Lawrence Berkeley National Laboratory
1 Cyclotron Road, M/S 33R0345
Berkeley, CA 94720
Tel: (510) 486-5709
Fax: (510) 486-5909


On Thu, Nov 1, 2018 at 5:07 AM David Waterman <dgwaterman@gmail.com> wrote:
Hi folks,

It's great to see the momentum building behind the project to migrate to Python 3. From the 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
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