Monday, June 18, 2012

Another year, another GSoC!

Well, this blog post took long enough, but I'm happy to announce that I've been accepted once again for the Google Summer of Code, this year for Twisted ("an event-driven networking engine written in Python"). What's more, my project is essentially the same as last year - porting Twisted to Python 3, or at least getting as close as possible (my actual proposal is available on Google Docs). Unfortunately, compared to last year, my school load was much higher this time around, so I've done much less work than I would have liked.

At the start, I've mostly focused on fixing the warnings thrown when running the test suite with "-3", taking care of most of the trivial ones (eg. has_key, apply, classical division). Currently, I'm looking into replacing "buffer()", which was a built-in but is removed in Python 3. While the work is similar, the workflow for getting changes in is quite different from SymPy. Twisted uses a svn repository, and trac for issue tracking; each change must be done in a separate branch and have a corresponding ticket; SymPy uses the classical Github + git workflow, with pull requests and reviews in the online interface. Now, I got too used to git to just give it up easily (especially as the Twisted workflow almost requires additional tools on top of vanilla svn), and this guide was very useful in setting up git svn. Although I'm getting used to the review process (eg. changesets are reviewed in total, not per-commit), I still find the Github (and git) model more productive - it streamlines review and allows small, atomic commits to be made (although I've been trying to keep my changes as small as possible, each such small change requires the opening of another ticket and creation of another SVN branch, so there's a point at which it's too much effort to do it all). Still, Twisted is unlikely to change so I will have to accommodate - at least I can follow my own practices in my own repo.

The next steps are deciding which porting strategy to ultimately pursue - some Twisted developers suggest a single code-base strategy (py2 and py3 compatible), I personally favor a single code base which relies on 2to3 for py3k compatibility and there was even an attempt at a dual code-base, by Antoine Pitrou. While I feel that approach is the least likely to succeed, as it introduces a high burden on the maintainer (and the effort has indeed stalled), the code already there will be helpful in my own work. Often, the changes made in py3k code can be reused in the "main", Python 2 code with little or no changes. Still, all approaches deserve investigation and my mind is still open to other ideas. Twisted currently supports Python 2.6+, which makes my job easier. The final piece of good news is that I may be able to get some sort of help (or at least support) from Canonical, as part of their plan to install only Python 3 in the next desktop Ubuntu release.

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