Difference between revisions of "Python3"

Revision as of 16:13, 28 February 2014

This page tracks the progress of Python 3 effort porting for OpenStack.

Python 3

Why should OpenStack move to Python 3 right now?

Python 3 is usually seen as the new Python version which breaks compatibility and raises new Unicode issues. Python 3 is much more than that. It’s a new clean language which has a more consistent syntax. It has many new features, not less than 15 new modules. Python 3 is already well supported by major Linux distributions, whereas Python 2.7 reached its end-of-life. Slowly, some bugs cannot be fixed in Python 2.7 anymore and are only fixed in the latest Python 3 release. Python 3 is now 5 years old and considered as a mature programming language.

Port Python 2 code to Python 3

OpenStack project chose to use the same code base for Python 2 and Python 3. The Six: Python 2 and 3 Compatibility Library helps to write code working on both versions.

References to port Python 2 code to Python 3

• Porting to Python 3 Book by Lennart Regebro, especially the Language differences and workarounds.
• HOWTO: Porting Python 2 Code to Python 3 by Brett Cannon
• Porting Python Code to 3.x
• python-incompatibility: Demonstrates incompatibilities between Python versions.

Common pitfalls

What is a string ?

You should definitely not talk about "strings" in your commit logs/reviews. In Python 2, a 'string' is bytes; in Python 3, it's a Unicode text string. The following code snippet may help in understanding the difference:

Python 2:

   >>> type('foo')
   <type 'str'>
   >>> type(u'foo')
   <type 'unicode'>
   >>> type(b'foo')
   <type 'str'>
   >>> isinstance('foo', six.text_type)
   False
   >>> isinstance(u'foo', six.text_type)
   True
   >>> bytes is str
   True
   >>> b'foo'[0]
   'f'

Python 3:

   >>> type('foo')
   <class 'str'>
   >>> type(u'foo')
   <class 'str'>
   >>> type(b'foo')
   <class 'bytes'>
   >>> isinstance('foo', six.text_type)
   True
   >>> isinstance(b'foo', six.text_type)
   False
   >>> bytes is str
   False
   >>> b'foo'[0]
   102

Python 3 of OpenStack Dependencies

Blocker Pointer: it's not yet possible to specify different list of dependencies for Python 2 and Python 3. For example, mox only works on Python 2, mox3 can be used on Python 3.

• Julien Danjou proposed to add requirements-py3.txt: openstack/requirements patch and openstack-dev/pbr patch
• An alternative is to support markers in requirements (in pip): pip issue: Support markers in setup(install_requires)?; Victor Stinner's pull request: "parse requirements in markers"

OpenStack Dependencies:

• mox: use mox3 or port tests on mock which works on Python 3 (mock has been integrated in Python 3.3 as unittest.mock)
• eventlet: not available on Python 3 yet, alternatives: asyncio (Tulip for Python 3.3+/Trollius for Python 2), Tornado

Portage in progress

• Oslo Messaging: Portage in Progress by Victor Stinner (dashboard)
• glanceclient: Portage in Progress by Cyril Roelandt (dashboard)
• heatclient: Portage in Progress by Cyril Roelandt (dashboard)
• neutronclient: Portage in Progress by Cyril Roelandt (dashboard)
• glanceclient: Portage in Progress by Cyril Roelandt (dashboard)

Portage done

• keystoneclient: Portage in Progress by Cyril Roelandt (dashboard)

Python 3 Status of OpenStack projects

See also Python3Deps.

OpenStack clients

Core OpenStack projects

Reports at OpenStack Summits

• Havana summit notes: https://etherpad.openstack.org/p/havana-python3
• Icehouse summit notes: https://etherpad.openstack.org/p/IcehousePypyPy3

Dependencies

This is an attempt to document which OpenStack dependencies work under Python 3. We're starting with oslo, since it's the base of everything else, then gradually including other projects.

The caniusepython3 tool can be used to do quick yes/no Python 3 support checks.

oslo.config

pip-requires

• argparse - included with Python 2.7+. The separate package is only needed for 2.6.

test-requires

• mox - mox3 supports Python, or replace mox with mock (which is now included in python 3.3)
• nose - supports Python 3
• nose-exclude - 2.6-2.7, 3.1-3.3
• testtools - 2.6-2.7, 3.2-3.3
• coverage - supports 2.3-3.3
• sphinx - supports Python 3

oslo-incubator

pip-requires

• PasteDeploy: supports 2.5-3.3
• WebOb: support Python 3
• eventlet: NO (MAJOR PAIN POINT) (gevent doesn't either, though there are some old forks that tried)
• greenlet: supports 2.4-3.2 (lack of 3.3 may be false negative)
• lxml: supports 2.4-3.3
• routes: supports 2.6-3.3
• iso8601: NO (perhaps try python-dateutil, specifically the parser module?)
• anyjson: 2.4-3.1 (lack of 3.2-3.3 may be false negatives)
• kombu: supports Python 3 (exact version not given)
• argparse: included in Python 2.7+
• stevedore: supports 2.7, 3.2, and 3.3
• SQLAlchemy: supports Python 3 (exact version not given)
• qpid-python: NO

test-requires

• distribute: 2.4-3.3
• coverage: 2.3-3.3
• fixtures: supports Python 3 (exact version not given)
• mock: 2.5-3.3
• mox: use mox3, or replace mox with mock (which is now included in python 3.3)
• mysql-python: NO (maybe try pymysql instead?)
• nose: Supports Python 3
• nose-exclude: 2.6-2.7, 3.1-3.3
• nosexcover: NO (bug in tracker from 2012-05; no comments)
• nosehtmloutput: ?
• pep8: Supports Python 3
• pyflakes: Supports Python 3
• pylint: Supports Python 3 (tested with Python 3.2)
• pyzmq: Supports 2.6-2.7, 3.2+
• redis: Supports 2.5-2.7, 3.2+
• setuptools-git: 2.4-2.7, 3.1-3.3
• sphinx: Supports Python 3
• testtools: 2.6-2.7, 3.2-3.3
• webtest: 2.6-2.7, 3.2-3.3