I propose porting cqlsh and cqlshlib to Python 3. End-of-life for Python 2.7 <https://legacy.python.org/dev/peps/pep-0373/> is currently planned for 1 January 2020. We should prepare to port the tool to a version of Python that will be officially supported.
I'm seeking input on three questions: - Should we port it to straight Python 3, or Python 2/3 cross compatible? - How much more testing is needed? - Can we wait until after 4.0 for this? I have an implementation <https://github.com/ptbannister/cassandra/tree/cqlshlib3> to go with my proposal. In parallel with getting the dtest cqlsh_tests working again, I ported cqlsh.py and cqlshlib to Python 3. It passes with almost all of the dtests and the unittests, so it's in pretty good shape, although it's not 100% done (more on that below). *Python 3 or 2/3 cross compatible?* There are plenty of examples of Python libraries that are compatible with both Python 2 and Python 3 (notably the Cassandra Python driver), so I think this is achievable. The question is, do we want to pay the price of cross compatibility? If we write cqlsh to be 2/3 cross compatible, we'll carry a long term technical debt to maintain that feature. The value of continuing to support Python 2 will diminish over time. However, a cross compatible implementation may ease the transition for some users, especially if there are users who have made significant custom modifications to the Python 2.7 implementation of cqlsh, so I think we must at least consider the question. *What additional testing is needed before we could release it?* I used coverage.py to check on the code coverage of our existing dtest cqlsh_tests and cqlshlib unittests. There are several blind spots in our current testing that should be addressed before we release a port of cqlsh. Details of this are available on JIRA ticket CASSANDRA-10190 <https://issues.apache.org/jira/browse/CASSANDRA-10190> in the attachment coverage_notes.txt <https://issues.apache.org/jira/secure/attachment/12926015/coverage_notes.txt>. Beyond that, I've made no efforts to test on platforms other than Ubuntu and CentOS, so Windows testing is needed if we're making efforts to support Windows. It would also be preferable for some real users to try out the port before it replaces the Python 2.7 cqlsh in a release. Besides this, there are a couple of test failures I'm still trying to figure out, notably tests involving user defined map types (a task made more interesting by Python's general lack of support for immutable map types). *Can we wait until after 4.0 for this?* I don't think it's reasonable to try to release this with 4.0 given the current consensus around a feature freeze in the next few months. My feeling is that our testers and committers are already very busy with the currently planned changes for 4.0. I recommend planning toward a release to occur after 4.0. If we run up against Python 2.7 EOL before we can cut the next release, we could consider releasing a ported cqlsh independently, for installation through distutils or pip. Patrick Bannister
