Python3
This page tracks the progress of Python 3 effort porting for OpenStack.
Contents
- 1 Python 3
- 2 Pycon Montreal 2014: Sprint Port OpenStack to Python 3
- 3 OpenStack Summit 2014 at Atlanta (Juno): The Future of Python Support
- 4 Port Python 2 code to Python 3
- 5 Python 3 of OpenStack Dependencies
- 6 Portage in progress
- 7 Portage done
- 8 Python 3 Status of OpenStack projects
- 9 Reports at OpenStack Summits
- 10 Dependencies
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.
Pycon Montreal 2014: Sprint Port OpenStack to Python 3
Enovance organizes a sprint to Port OpenStack to Python 3 during 4 days: between April, 14 (Monday) and April, 17 (Thursday). See the page Python3/SprintPycon2014.
OpenStack Summit 2014 at Atlanta (Juno): The Future of Python Support
Doug Hellmann proposed a cross-project workshop: http://summit.openstack.org/cfp/details/316
Etherpad: https://etherpad.openstack.org/p/juno-cross-project-future-of-python
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. OpenStack must still support Python 2.6 for RHEL, but not Python 2.5 and older. Debian Stable provides Python 3 but only Python 3.2, so u'unicode' syntax should be avoided (use six.u('unicode') instead).
Common patterns
- Replace dict.iteritems() with six.iteritems(dict)
- Replace iterator.next() with next(iterator)
- Replace basestring with six.string_types
- Replace unicode with six.text_type
bytes.decode and unicode.encode
Python has a notion of "default encoding": sys.getdefaultencoding(). On Python 2, the default encoding is ASCII, whereas it is UTF-8 on Python 3.
Don't write data.decode()
or text.encode()
without parameter, because you will use a different encoding on Python 2 and Python 3.
Use an explicit encoding instead. Example: data.decode('utf-8')
or text.encode('utf-8')
. The right encoding depends on the use case, but UTF-8 is usually a good candidate (it is a superset of ASCII).
safe_decode
Olso Incubator has a function safe_decode() which can be used to decode a bytes string and pass text strings unchanged.
The default encoding is sys.stdin.encoding or sys.getdefaultencoding()
:
- Python 3: the locale encoding, or UTF-8 if sys.stdin is "mocked" (io.StringIO instance)
- Python 2: the locale encoding, or ASCII if stdin is not a TTY or if sys.stdin is "mocked" (StringIO.StringIO instance)
It's safer to explicit the encoding to not rely on the locale encoding and have the same behaviour even if sys.stdin is "mocked".
Safe usage:
-
safe_decode(data, 'utf-8')
: decode bytes from UTF-8 or returns data unchanged if it's already a text string
Unsafe usage:
-
safe_decode(data)
By default, the decoder is strict. You can specify a different error handler using the optional errors
parameter. Example: safe_decode(b'[\xff]', 'ascii', 'ignore') returns '[]'.
safe_encode
Olso Incubator has a function safe_encode() which can be used to encode a string. Its usage is tricky and you should understand how it works and which encodings are used.
-
safe_encode(text)
encodes text to the output encoding -
safe_encode(bytes)
may decode the string and then reencode to a different encoding if input and output encodings are different
The default input encoding (incomding
parameter) is sys.stdin.encoding or sys.getdefaultencoding()
:
- Python 3: the locale encoding, or UTF-8 if sys.stdin is "mocked" (io.StringIO instance)
- Python 2: the locale encoding, or ASCII if stdin is not a TTY or if sys.stdin is "mocked" (StringIO.StringIO instance)
The default output encoding (encoding
parameter) is UTF-8.
It's safer to explicit the input encoding to not rely on the locale encoding and have the same behaviour even if sys.stdin is "mocked".
Safe usage:
-
safe_encode(data, incoming='utf-8')
: encode text to UTF-8 or returns data unchanged if it's already a bytes string (since the input and output encoding are UTF-8)
Unsafe usage:
-
safe_encode(data)
Example:
-
safe_encode(b'\xe9', incoming='latin-1')
returnsb'\xc3\xa9'
.
By default, the encoder and the decoder are strict. You can specify a different error handler using the optional errors
parameter. Example: safe_encode(b'[\xff]', incoming='ascii', errors='ignore')
returns b'[]'
.
HTTP
The HTTP protocol is based on bytes:
- HTTP body contains bytes. For example, use io.BytesIO for a stream storing an HTTP body.
- HTTPConnection.getresponse().read() returns bytes (in Python 3, str which is bytes in Python 2)
- On Python 3, the http.client accepts text for HTTP headers: keys are encoded to ASCII and values to ISO 8859-1 (which is only a small subset of the Unicode charset)
- It looks like Swift encodes internally HTTP headers to UTF-8 (directly using the UTF-8 encoding, not using a MIME encoding like =?UTF-8?Q?...?=. See the HTTP [RFC 2047 http://www.ietf.org/rfc/rfc2047.txt] and HTTP header should use what character encoding?
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.
Oslo Incubator
BLOCKER BUG: Tests using testscenarios fail on Python 3 with nosetests because of this bug: https://bugs.launchpad.net/testscenarios/+bug/872887
Recently merged reviews:
Test (full path) | Patches | Comment | |
---|---|---|---|
tests/unit/config/test_generator.py | https://review.openstack.org/#/c/88087/ | ||
tests/unit/crypto/test_utils.py | https://review.openstack.org/87413 | ||
tests/unit/db/sqlalchemy/test_migration_common.py | |||
tests/unit/db/sqlalchemy/test_migrate.py | |||
tests/unit/db/sqlalchemy/test_models.py | https://review.openstack.org/#/c/80307/ | ||
tests/unit/db/sqlalchemy/test_options.py | https://review.openstack.org/#/c/80627/ | ||
tests/unit/db/sqlalchemy/test_migrate_cli.py | |||
tests/unit/db/sqlalchemy/test_utils.py | |||
tests/unit/db/sqlalchemy/test_sqlalchemy.py | |||
tests/unit/fixture/test_logging.py | https://review.openstack.org/#/c/90318/ | ||
tests/unit/middleware/test_request_id.py | https://review.openstack.org/#/c/80336/ | ||
tests/unit/middleware/test_sizelimit.py | https://review.openstack.org/#/c/80450/ | ||
tests/unit/middleware/test_audit.py | depends on pycadf | ||
tests/unit/reports/test_guru_meditation_report.py | https://review.openstack.org/#/c/87404/ | ||
tests/unit/reports/test_base_report.py | https://review.openstack.org/#/c/87973/ | ||
tests/unit/reports/test_openstack_generators.py | https://review.openstack.org/#/c/88124/ | ||
tests/unit/reports/test_views.py | https://review.openstack.org/87376 | ||
tests/unit/rpc/test_common.py | https://review.openstack.org/#/c/80533/ | The RPC code in the incubator is deprecated in favor of oslo.messaging. --doug-hellmann (talk) 15:40, 14 April 2014 (UTC) | |
tests/unit/scheduler/test_base_filter.py | https://review.openstack.org/#/c/80321/ | ||
tests/unit/scheduler/test_weights.py | https://review.openstack.org/#/c/87336/ | ||
tests/unit/test_cliutils | https://review.openstack.org/#/c/74433/ | ||
tests/unit/test_fileutils | https://review.openstack.org/#/c/74728/ | ||
tests/unit/test_gettext.py | https://review.openstack.org/#/c/80534/ | ||
tests/unit/test_imageutils.py | https://review.openstack.org/#/c/90532/ | ||
tests/unit/test_jsonutils.py | https://review.openstack.org/#/c/80370/ | ||
tests/unit/test_log.py | depends on https://review.openstack.org/#/c/80534/ | ||
tests/unit/test_quota.py | https://review.openstack.org/#/c/80564/ | ||
tests/unit/test_strutils.py |
OpenStack clients
Project | Python 3 compatibility | CI tests running? | Python 3 classifiers ? | Blocked by | Comment |
---|---|---|---|---|---|
python-ceilometerclient | Yes | Voting | On PyPI | ||
python-cinderclient | Yes | Voting | On PyPI | ||
python-ganttclient | ? | ? | ? | ? | |
python-glanceclient | In Progress | Non-voting | No | ||
python-heatclient | Yes | Voting | On PyPI | ||
python-ironicclient | Yes | Voting | On PyPI | ||
python-keystoneclient | Yes | Voting | On PyPI | ||
python-marconiclient | Yes | Voting | Yes | ||
python-melangeclient | ? | ? | ? | ||
python-novaclient | Yes | Voting | In the Git repo, not on PyPI | ||
python-neutronclient | In progress | Non-voting | Differences between Python 2 and 3 | ||
python-openstackclient | In Progress | Non-Voting | No | Works with glanceclient HEAD | |
python-savannaclient | In progress | Non-voting | https://review.openstack.org/#/c/73128/ | ||
python-swiftclient | In progress | Non-voting | `No | Differences between Python 2 and 3 | |
python-tuskarclient | Yes | Voting | On PyPI | ||
python-troveclient | Yes | Voting | On PyPI |
Core OpenStack projects
Project | Python 3 compatibility | CI tests running? | Trove classifiers | Blocked by | Comment |
---|---|---|---|---|---|
ceilometer | No | No | No |
|
|
cinder | No | No | No |
|
|
glance | No | No | No |
|
|
heat | No | No | No |
|
|
horizon | No | No | No |
|
|
keystone | No | No | No |
|
|
neutron | No | No | No |
|
|
nova | No | No | No |
|
|
swift | No | No | No |
|
Dependencies
Project | Python 3 compatibility | CI tests running? | Python 3 classifiers ? | Blocked by | Comment |
---|---|---|---|---|---|
boto | No | N/A | No | See https://github.com/boto/boto3 (experimental) | |
django-compressor | No | No | No | https://github.com/django-compressor/django-compressor/issues/484 | |
django-openstack-auth | No | No | No | Ported: https://review.openstack.org/#/dashboard/8122 | |
dnspython | Yes | N/A | Yes | Must use the Python 3 version, see https://github.com/rthalley/dnspython/issues/60 | |
ecdsa | Yes | N/A | In the Git repo | Py3 support merge before the 0.10 release (see https://github.com/warner/python-ecdsa/commits/master) | |
eventlet | No | No | No | Victor Stinner is working on Trollius (asyncio for Python 2) which may replace eventlet: Use the new asyncio module and Trollius in OpenStack | |
hacking | No | No | No | Cyril Roelandt patch: Make hacking Python 3 compatible | |
jsonrpclib | No | N/A | No | The project seems dead :( | |
mysql-python | No | No | No | 2 pull requests for Python 3 (https://github.com/farcepest/MySQLdb1/pulls). The projects is being renamed to moist (https://github.com/farcepest/moist), Python 3 support might happen there. | |
netifaces | No | N/A | No | Patch sent by Victor Stinner (in private): netifaces_python3.patch, Debian has patches too | |
nose-exclude | No | No | No | https://bitbucket.org/kgrandis/nose-exclude/issue/10/test-failures-with-python-3 | |
nosehtmloutput | No | No | No |
|
|
nosexcover | No | N/A | On PyPI | Python 3 support since 1.0.9 | |
openstack.nose-plugin | No | No | No | ||
oslo.vmware | No | Voting | Yes | suds | |
oslo.config | Yes | Voting | In the git repo, not on PyPI | ||
oslo.messaging | No | No | No | ||
oslo.rootwrap | Yes | Yes | In the Git repo, not on PyPI (1.1.0) | ||
oslosphinx | Yes | No tests :) | In the git repo, not on PyPI | https://review.openstack.org/#/c/79311/ | |
oslo.sphinx | No | No | No | Must be replaced by oslosphinx (without the dot) | |
pam | No | No | No | The fork simplepam works on Python 2 and 3 | |
paramiko | Yes | N/A | On PyPI | Get https://review.openstack.org/#/c/81132/ merged | |
paste | No | No | No | https://bitbucket.org/ianb/paste/pull-request/9/python-3-support/diff | |
pycadf | No | No | No | ||
python-ldap | No | No | No | The project seems dead. | |
qpid-python | No | No | No | ||
rtslib-fb | No | No | No | ||
sphinxcontrib-docbookrestapi | No | No | No | ||
sphinxcontrib-httpdomain | No | No | No | ||
sphinxcontrib-pecanwsme | No | No | No | ||
sqlalchemy-migrate | No | No | No |
|
|
suds | No | No | No | Dead project | |
taskflow | Yes | Yes | Yes | ||
thrift | No | No | No | ||
websockify | No | No | No |
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
- 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