Status of the CubicWeb python3 porting effort, February 2016

An effort to port CubicWeb to a dual python 2.6/2.7 and 3.3+ code base was started by Rémi Cardona in summer of 2014. The first task was to port all of CubicWeb's dependencies:

• logilab-common 0.63
• logilab-database 1.14
• logilab-mtconverter 0.9
• logilab-constraint 0.6
• yams 0.40
• rql 0.34

Once that was out of the way, we could start looking at CubicWeb itself. We first set out to make sure we used python3-compatible syntax in all source files, then started to go and make as much of the test suite as possible pass under both python2.7 and python3.4. As of the 3.22 release, we are almost there. The remaining pain points are:

• cubicweb's setup.py hadn't been converted. This is fixed in the 3.23 branch as of https://hg.logilab.org/master/cubicweb/rev/0b59724cb3f2 (don't follow that link, the commit is huge)
• the CubicWebServerTC test class uses twisted to start an http server thread, and twisted itself is not available for python3
• the current method to serialize schema constraints into CWConstraint objects gives different results on python2 and python3, so it needs to be fixed (https://www.logilab.org/ticket/296748)
• various questions around packaging and deployment: what happens to e.g. the cubicweb-common package installing into python2's site-packages directory? What does the ${prefix}/share/cubicweb directory become? How do cubes express their dependencies? Do we need a flag day? What does that mean for applications?