Difference between revisions of "Python3"
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Revision as of 11:50, 6 March 2015
This page tracks the progress of Python 3 effort porting for OpenStack.
Contents
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. OpenStack supported Python 2.6 for RHEL up to Juno, 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'[]'
.
logging module and format exceptions
On Python 2, the logging module accepts bytes and text strings. On Python 3, it only accepts text strings. For example, logging.error(b'hello') logs b'hello'
instead of 'hello'
.
There is no clear rule for format exceptions yet. There are different choices depending on the project:
-
str(exc)
: native string, so use bytes on Python 2 -
six.text_type(exc)
: always use Unicode. It may raise unicode error depending on the exception, be careful. Example of such error in python 2:unicode(Exception("nonascii:\xe9"))
. -
six.u(str(exc))
: unsafe on Python 2 if str(exc) contains non-ASCII bytes, ex:unicode(str(Exception("\xff")))
-
LOG.exception(_LE("... %(exc)s ..."), {"exc": exc, ...})
Since logging functions expect text strings on Python 3, logged exceptions should be formatted using str(exc)
. Example: LOG.debug(str(exc))
.
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
tox/testr error: db type could not be determined
The "db type could not be determined" error comes from .testrepository/times.dbm used by testr.
Workaround: "rm -rf .testrepository/".
Python 3 Status of OpenStack projects
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 | https://review.openstack.org/#/c/107752/ | ||
tests/unit/db/sqlalchemy/test_migrate.py | https://review.openstack.org/#/c/107921/ | ||
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 | https://review.openstack.org/107988 | ||
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 | https://review.openstack.org/104890 | ||
tests/unit/test_processutils.py | processutils was moved to the new oslo.concurrency project | ||
tests/unit/test_quota.py | https://review.openstack.org/#/c/80564/ | ||
tests/unit/test_strutils.py |
Common Libraries (Oslo Projects)
For the list of Common Libraries, see http://git.openstack.org/cgit/openstack/governance/tree/reference/programs.yaml#n160
Project | Python 3 compatibility | Comment |
---|---|---|
cliff | Yes | |
oslo.concurrency | Partial | https://review.openstack.org/141206 |
oslo.config | Yes | |
oslo.db | Partial | No unit tests with MySQL because of DB driver |
oslo.i18n | Yes | |
oslo.log | Yes | |
oslo.messaging | Yes | eventlet executor and qpid driver are not supported on Python 3, greenio
executor may help |
oslo.middleware | Yes | |
oslo.rootwrap | Yes | |
oslo.serialization | Yes | |
oslosphinx | ? | The project only contains two short .py files, it looks to be Python 3 compatible. Is Sphinx Python 3 compatible? |
oslotest | Yes | |
oslo.versionedobjects | Yes | |
oslo.vmware | No | Blocked suds dependency |
oslo.utils | Yes | |
oslo.version | Yes | not released on PyPI yet |
pylockfile | Yes | related to https://pypi.python.org/pypi/lockfile ? |
stevedore | Yes | |
taskflow | Yes |
Development tools:
Project | Python 3 compatibility | Comment |
---|---|---|
cookiecutter | ? | |
oslo-cookiecutter | ? | |
hacking | ? | |
pbr | ? |
OpenStack clients
Project | Python 3 compatibility | CI tests running? | Python 3 classifiers ? | Blocked by | Comment |
---|---|---|---|---|---|
python-barbicanclient | Yes | Voting | In the git repo, not on PyPI | ||
python-ceilometerclient | Yes | Voting | On PyPI | ||
python-cinderclient | Yes | Voting | On PyPI | ||
python-ganttclient | ? | ? | ? | ? | |
python-glanceclient | Yes | Voting | On PyPI | ||
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 | On PyPII | ||
python-neutronclient | Not released yet | Voting | Yes | ||
python-openstackclient | OK | Voting | Yes | As of 0.9 | |
python-saharaclient | In progress | Non-voting | https://review.openstack.org/#/c/73128/ | ||
python-swiftclient | Yes | Voting | On PyPI | ||
python-tuskarclient | Yes | Voting | On PyPI | ||
python-troveclient | Yes | Voting | On PyPI |
Core OpenStack projects
Completely updated on Monday, September the 29th.
Project | Python 3 compatibility | CI tests running? | Trove classifiers | Blocked by | Comment |
---|---|---|---|---|---|
ceilometer | No | No | No |
Requirements
Requirements for tests
|
|
cinder | No | No | No |
Requirements
Requirements for tests
|
|
glance | No | No | No |
Requirements
Requirements for tests
|
|
heat | No | No | No |
Requirements
Requirements for tests
|
|
horizon | No | No | No |
Requirements
Requirements for tests
|
|
keystone | No | No | No |
Requirements for tests
|
|
neutron | No | No | No |
Requirements
|
|
nova | No | No | No |
Requirements for tests
|
|
swift | No | No | No |
Requirements
Requirements for tests
|
Number of core OpenStack projetcs blocked by each dependency:
9 eventlet 7 oslo.messaging 7 oslo.db 6 sqlalchemy-migrate 6 paste 5 python-neutronclient 5 mysql-python 2 suds 2 qpid-python 2 python-saharaclient 2 pycadf 2 openstack.nose_plugin 2 nosehtmloutput 1 xstatic-spin 1 xstatic-rickshaw 1 xstatic-qunit 1 xstatic-jsencrypt 1 xstatic-jquery.tablesorter 1 xstatic-jquery.quicksearch 1 xstatic-jquery-migrate 1 xstatic-jquery 1 xstatic-jasmine 1 xstatic-hogan 1 xstatic-font-awesome 1 xstatic-d3 1 xstatic-bootstrap-datepicker 1 xstatic-angular-mock 1 xstatic-angular-cookies 1 xstatic-angular 1 xstatic 1 websockify 1 thrift 1 sphinxcontrib-pecanwsme 1 sphinxcontrib-httpdomain 1 sphinxcontrib-docbookrestapi 1 rtslib-fb 1 python-ldap 1 python-barbicanclient 1 nose-exclude 1 nodeenv 1 libvirt-python 1 ldappool 1 jsonrpclib 1 glance_store 1 django-pyscss 1 croniter
Dependencies
Porting status for global-requirement.txt.
It's now possible to specify different dependencies for Python 2 and Python 3 using:
- requirements-py2.txt: all dependencies for Python 2 (not only dependencies specific to Python 2)
- requirements-py3.txt: all dependencies for Python 3 (not only dependencies specific to Python 3)
- (same for test-requirements.txt)
You have to edit tox.ini to specify the right requirements file. Extract of a tox.ini file:
... [testenv:py33] deps = -r{toxinidir}/requirements-py3.txt -r{toxinidir}/test-requirements-py3.txt ...
See also a patch 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). Examples:
- neutronclient: https://review.openstack.org/#/c/95786/
- Oslo Incubator: https://review.openstack.org/#/c/93729/
Project | Python 3 compatibility | CI tests running? | Python 3 classifiers ? | Blocked by | Comment |
---|---|---|---|---|---|
boto | Yes | N/A | Yes | See https://github.com/boto/boto3 (experimental) <- This seems dead, and https://github.com/boto/boto works with Python 3.x (since 2.32). | |
django-compressor | Yes | N/A | Yes | Requirements upgraded: https://review.openstack.org/94357 | |
django-openstack-auth | Yes | N/A | Yes |
As of 1.1.6 | |
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 | eventlet portage to Python 3 in progress: eventlet issue #6: Support Python 3.3 and Pull request #99: Fix several issues with python3 thread patching. 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 | Yes | N/A | Yes | Patch sent by Victor Stinner (in private): netifaces_python3.patch, Debian has patches too. Python 3 support as of 0.10.4. Pushed to requirements: https://review.openstack.org/94358 . | |
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 | On PyPI | ||
oslo.messaging | No | No | No | Portage in Progress by Victor Stinner (dashboard) | |
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 | Requirements upgraded: https://review.openstack.org/#/c/81132/ | |
paste | No | No | No | https://bitbucket.org/ianb/paste/pull-request/9/python-3-support/diff | |
pycadf | No | No | No | Classifiers added https://review.openstack.org/#/c/133088/ | |
python-ldap | No | No | No | The project seems dead. | |
python-memcached | Not released, but last commit on git has it | No | No | Issue #52: Python 3.3 support? , Pull request #26: Python 3.3 Support -- Julien Danjou ported pymemcache to Python 3, another memcached client, he suggests to use this one instead | |
qpid-python | No | No | No | ||
rtslib-fb | No | No | No | ||
sphinxcontrib-docbookrestapi | Yes | Yes | Yes | Support for 3.3, but not for 3.4, PyPI not updated. | |
sphinxcontrib-httpdomain | No | No | No | ||
sphinxcontrib-pecanwsme | No | No | No | ||
sqlalchemy-migrate | No | No | No |
|
|
suds | No | No | No | "Lightweight SOAP client". Last commit 2 years ago: https://fedorahosted.org/suds/browser See also this fork which is promising: https://bitbucket.org/jurko/suds | |
taskflow | Yes | Yes | Yes | ||
thrift | No | No | No | ||
websockify | No | No | No |
Other OpenStack projects
Python 3 compatible:
- stackforge/python-jenkins : https://review.openstack.org/#/c/95004/ (py33 gate is voting)
- openstack-infra/jenkins-job-builder : https://review.openstack.org/87810 (Python 3 support finally merged in, Sept. 2014)
Reports at OpenStack Summits
- Havana summit notes: https://etherpad.openstack.org/p/havana-python3
- Icehouse summit notes: https://etherpad.openstack.org/p/IcehousePypyPy3
- Juno summit notes: https://etherpad.openstack.org/p/juno-cross-project-future-of-python (Oslo) and https://etherpad.openstack.org/p/juno_swift_python3 (Swift)
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.