Implement PEP 495 (Local Time Disambiguation)

[abalkin]

BPO	24773
Nosy	@tim-one, @abalkin, @vstinner, @4kir4, @vadmium, @koobs
Superseder	bpo-27595: Document PEP 495 (Local Time Disambiguation) features
Files	ltdf.patch: Initial pure python implementation ltdf-2.patch issue24773-s3.diff issue24773-s3-2.diff issue24773-s3-3.diff issue24773-s3-4.diff issue24773-final.diff koobs-freebsd-current-usr-share-zoneinfo.txt

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/abalkin'
closed_at = <Date 2016-08-23.20:39:56.449>
created_at = <Date 2015-08-01.19:17:27.574>
labels = ['extension-modules', 'type-feature', 'library']
title = 'Implement PEP 495 (Local Time Disambiguation)'
updated_at = <Date 2017-01-04.11:55:55.415>
user = 'https://github.com/abalkin'

bugs.python.org fields:

activity = <Date 2017-01-04.11:55:55.415>
actor = 'vstinner'
assignee = 'belopolsky'
closed = True
closed_date = <Date 2016-08-23.20:39:56.449>
closer = 'belopolsky'
components = ['Extension Modules', 'Library (Lib)']
creation = <Date 2015-08-01.19:17:27.574>
creator = 'belopolsky'
dependencies = []
files = ['40094', '40096', '40614', '43753', '43778', '43781', '43836', '43850']
hgrepos = ['335']
issue_num = 24773
keywords = ['patch']
message_count = 48.0
messages = ['247819', '247831', '251811', '270574', '270776', '270797', '271039', '271040', '271048', '271063', '271073', '271081', '271086', '271087', '271127', '271128', '271147', '271166', '271167', '271178', '271192', '271229', '271233', '271234', '271239', '271300', '271313', '271315', '271318', '271393', '271396', '271413', '271414', '271473', '271559', '271695', '271696', '271734', '272398', '272448', '272449', '272452', '272489', '272568', '273003', '273515', '284627', '284632']
nosy_count = 8.0
nosy_names = ['tim.peters', 'belopolsky', 'vstinner', 'stub', 'akira', 'python-dev', 'martin.panter', 'koobs']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = '27595'
type = 'enhancement'
url = 'https://bugs.python.org/issue24773'
versions = ['Python 3.6']

[abalkin]

Adds a boolean member to the instances of datetime.time
and datetime.datetime classes that can be used to differentiate
between two moments in time for which local times are the same.

See Datetime-SIG "Local time disambiguation proposal" discussion 1 for more details.

[abalkin]

Something went wrong in my hg clone and Rietveld did not like my patch. I moved my development branch to github:

https://github.com/abalkin/cpython/tree/ltdf

Please feel free to leave your comments there.

[abalkin]

Changing the title to reference PEP-495.

[abalkin]

Submitting the latest Github snapshot as a patch against master for review. See bpo-24773-s3-2.diff.

[abalkin]

Naoki, thanks for the review. I addressed your comments in

https://github.com/abalkin/cpython/commit/a61a25d2dd04336361b2ea676c80afdb2639f579

Attached patch, bpo-24773-s3-3.diff, incorporates your comments and a few other fixes. See github for the full history.

[abalkin]

The new patch passes test_datetime on Windows. This was the last stumbling block for me to commit this patch. Unless anyone would ask for more time to review, I plan to commit later this week.

[abalkin]

I am posting the final version of the patch complete with the NEWS entry. Compared with the previous patch, bpo-24773-final.diff contains a fix for a reference leak.

I would like to use this opportunity to thank Zachary Ware for providing a Windows VM with a complete Python development setup, as well as everyone who participated in PEP-495 discussions and code reviews.

[python-dev]

New changeset 7c0917670ab8 by Alexander Belopolsky in branch 'default':
Closes issue bpo-24773: Implement PEP-495 (Local Time Disambiguation).
https://hg.python.org/cpython/rev/7c0917670ab8

[vadmium]

This upset the buildbots:

http://buildbot.python.org/all/builders/PPC64%20Fedora%203.x/builds/1259/steps/test/logs/stdio
======================================================================
FAIL: test_all (test.datetimetester.ZoneInfoCompleteTest)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/shager/cpython-buildarea/3.x.edelsohn-fedora-ppc64/build/Lib/test/datetimetester.py", line 4784, in test_all
    self.assertTrue(result.wasSuccessful(), name + ' ' + suffix)
AssertionError: False is not true : Africa/El_Aaiun system_transitions