Porting the Neutron Core to Python 3

https://blueprints.launchpad.net/neutron/+spec/neutron-python3

Problem Description

Neutron currently only works with Python 2.x. As some OpenStack projects now work with Python 3 (most of the Python clients, some of the oslo libraries...), and since OpenStack should move to Python 3 [1], Neutron shall be ported to Python 3.4.

Proposed Change

This specification details the steps needed to port Neutron core to Python 3.

The goal here is only to be able to run all the unit tests with Python 3.4. This may not be enough to make sure that Neutron is fully compatible with Python 3.4: we will also need to run Neutron in a devstack that uses Python 3.x, but this is another issue.

Obviously, these changes must not break any of Neutron’s reverse dependencies.

Data Model Impact

None

REST API Impact

None

Security Impact

None

Notifications Impact

None

Other End User Impact

None

Performance Impact

None

IPv6 Impact

None

Other Deployer Impact

If deployers want to run services under Python 3, they should install Python 3 with the whole stack. There will not be any differences for those who want to stick to Python 2, as we will make sure not to break anything.

Developer Impact

Once Neutron has been ported to Python 3, developers will not able to write code that only works with Python 2, since the py34 gate will be voting.

Community Impact

None

Alternatives

None

Implementation

Assignee(s)

Primary assignee:
cyril-roelandt

Work Items

  • Fix issues with the dependencies that are not Python 3 compatible: see the “Dependencies” section.
  • Make sure “tox -epy34” only runs tests that are specifically listed in tox.ini.
  • Enable the py34 gate in Neutron and make it voting. We should now be able to avoid regressions while working.
  • Fix the most obvious issues (print statements, failing imports, ...) that can probably be caught by 2to3. Checks for these might be added to tools/misc-sanity-checks.sh to avoid regressions. Once the py34 is voting and all the unit tests pass on Python 3, we will be able to remove them.
  • Fix all the tests, one by one.
  • Once they all work, remove the explicit list of tests to run when using Python 3 from tox.ini and add py34 to the default env list.

Dependencies

Neutron has dependencies on packages that currently do not work with Python 3:

  • oslo.db: Works with Python 3.4, even though we need a new release. The only issue is MySQL-Python which is not Python 3 compatible yet, but one can use mysqlclient as a drop-in replacement (MySQL-Python + py3 support + fixes).
  • olso.messaging: Thanks to the work of Victor Stinner, the RabbitMQ and ZMQ drivers and all the executors work on Python 3. Only the Qpid and AMQP 1.0 drivers don’t work on Python 3, but it should not block porting Neutron to Python 3. Currently, this work can only be found in the git repository, but a Python3-compliant version should be released in a near future.

All in all, there is probably no major issue with the dependencies.

Testing

Tempest Tests

None

Functional Tests

None

API Tests

None

Documentation Impact

User Documentation

None

Developer Documentation

Developers might be interested in reading the official Python 3 page on the Openstack wiki [2]. It shows the current progress and details some common issues that arise when porting code to Python 3.