17efb82eef
Pypi url changed from [1] to [2] [1] https://pypi.python.org/pypi/<package> [2] https://pypi.org/project/<package> Change-Id: I45ec295f5e8f338789f14c235a4ea9ab595f565a
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=================================
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Adding Python 3.4 support to Nova
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=================================
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https://blueprints.launchpad.net/nova/+spec/nova-python3
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Problem description
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===================
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It's time to add Python 3 support to Nova by generalizing the usage of the six
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module, in addition to the Python 2 support.
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Use Cases
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----------
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See the article `Why should OpenStack move to Python 3 right now?
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<http://techs.enovance.com/6521/openstack_python3>`_ for the rationale.
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Project Priority
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-----------------
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None
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Proposed change
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===============
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This specification details the steps needed to add Python 3.4 support to Nova
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by generalizing the usage of the six module.
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Almost all Nova dependencies are ported to Python 3. For the few remaining
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libraries, the port is in progress and should be done in a few weeks. It is
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already possible to start porting Nova to Python 3. See the Dependencies
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section below for more information.
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The goal here is to make all Nova tests pass with Python 3: Nova unit tests and
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Tempest tests.
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.. note::
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Python 2 support is kept.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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None (changes must not impact the data model).
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REST API impact
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---------------
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None (changes must not impact the REST API).
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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There is no impact on performances.
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In March 2013, Brett Canon ran `the official Python benchmarks suite
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<https://hg.python.org/benchmarks>`_ to compare Python 2.7 and 3.3 for his talk
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at Pycon US: `Python 3.3: Trust Me, It's Better Than Python 2.7
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<https://speakerdeck.com/pyconslides/python-3-dot-3-trust-me-its-better-than-python-2-dot-7-by-dr-brett-cannon>`_.
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The result: "If you sorted all of the benchmarks and looked at the median
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result ... Python 3 is the same".
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See the "Optimizations" section of each "What's New in Python 3.x" document for
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the full list of optimizations: `Python 3.1
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<https://docs.python.org/3/whatsnew/3.1.html#optimizations>`_, `Python 3.2
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<https://docs.python.org/3/whatsnew/3.2.html#optimizations>`_, `Python 3.3
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<https://docs.python.org/3/whatsnew/3.3.html#optimizations>`_ and `Python 3.4
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<https://docs.python.org/3/whatsnew/3.4.html#significant-optimizations>`_.
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Other deployer impact
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---------------------
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Deployers using python 2.7 will see no changes.
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Those able to run python 3.4 will now be try that out.
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Developer impact
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----------------
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Once the Python 3 check job becomes voting, developers will have to write code
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compatible with Python 2 and Python 3. During the transition period, only code
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tested by the ``tox.ini`` whitelists will require Python 3 support.
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Thanks to tox, it is trivial to run locally the Nova test suite on Python
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2.7 and 3.4.
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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victor-stinner
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Other contributors:
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None
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Work Items
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----------
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* Fix most obvious Python 3 issues. Example of a patch fixing most Python 3
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issues: `Port Nova to Python 3
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<https://github.com/haypo/nova/commit/bad54bc2b278c7c7cb7fa6cc73d03c70138bd89d>`_.
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This change is just a draft to test if porting Nova is feasible, it
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should be splitted into smaller patches grouped by similar changes. See also
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the `Port Python 2 code to Python 3
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<https://wiki.openstack.org/wiki/Python3#Port_Python_2_code_to_Python_3>`_
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section of the Python 3 wiki page.
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* Add a Python 3 test environment to ``tox.ini`` to run a subtest of the tests
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which pass on Python 3. It will use a whitelist of tests which are know to
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pass on Python 3.
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* Add a non-voting Python 3 check job for Nova
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* When the Python 3 check job is stable enough, make it voting. From this
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point, we should now be able to avoid Python 3 regressions while working.
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* Fix failing tests, one by one, to enlarge the whitelist of tests
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in ``tox.ini``.
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* Once all tests work, remove the whitelist of tests from ``tox.ini``.
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The transition period, when Python 3 is only supported partially, should be a
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short as possible.
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No voting Python 3 gate jobs will be added to not waste resources of the
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OpenStack infra, Python 2 gate jobs are enough. We consider that there is a low
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risk of having a Python 3 specific issue introduced by a conflict between the
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Python 3 check job and the Python 2 gate job.
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Dependencies
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============
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Remaining dependencies not compatible with Python 3 yet:
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* ``oslo.messaging``: The development version works on Python 3, except of Qpid
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and AMQP 1.0 drivers. To begin the Nova port to Python 3, we can start with
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the RabbitMQ driver, until AMQP is ported to Python 3 too. A new version
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of ``oslo.messaging`` will be released in a few weeks.
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* ``mysql-python``: the fork `mysqlclient
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<https://pypi.org/project/mysqlclient>`_ works on Python 3 and includes
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bug fixes. There is also `PyMySQL <https://pypi.org/project/PyMySQL>`_,
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a driver fully implemented in Python which works on Python 3 too, but it has
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worse performances.
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* ``python-memcached``: see the pull request `Port memcache to Python 3
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<https://github.com/linsomniac/python-memcached/pull/67>`_. It blocks
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``keystonemiddleware``. It may be replaced with ``pymemcache`` which is
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already Python 3 compatible.
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* ``websockify``: Python 3 classifier is missing in websockify 0.6.0, but it
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is present in the development version. Tests are failing but they may be
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issues with the tests, not with websockify directly.
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All in all, there is no major issue with the dependencies.
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Using the development version of ``oslo.messaging``, it's already possible to
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work on fixing Nova tests on Python 3.
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Testing
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=======
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The current test suite should be enough to test Nova on Python 3.
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We will run tests with Nova running under Python 3.4 by the end of this
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process: Nova unit tests and Tempest tests.
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Documentation Impact
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====================
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Developers might be interested in reading the official `Python 3 page
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<https://wiki.openstack.org/wiki/Python3>`_ on the Openstack wiki. It shows
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the current progress of the OpenStack port of Python 3, and details some common
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issues that arise when porting code from Python 2 to Python 3.
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References
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==========
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* Related Liberty specifications:
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- Heat: `Add Python 3.4 support <https://review.openstack.org/#/c/175340/>`_
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by Sirushti Murugesan
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- Neutron: `Porting to Python 3 spec
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<https://review.openstack.org/#/c/172962/>`_ by Cyril Roelandt with the
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support of Ihar Hrachyshka.
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* `Python 3 page in OpenStack wiki <https://wiki.openstack.org/wiki/Python3>`_
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Liberty
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- Introduced
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