datetime.strftime("%Y") not consistent for years < 1000

[florentx]

BPO	13305
Nosy	@jaraco, @abalkin, @vstinner, @ned-deily, @ezio-melotti, @florentx, @vadmium, @elenaoat, @pganssle, @Fronkan
Superseder	bpo-3173: external strftime for Python?
Files	issue13305_xmlrpc_patch.diff doc.patch issue13305.diff

^{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 = None
closed_at = None
created_at = <Date 2011-10-31.20:12:37.023>
labels = ['easy', 'type-bug', '3.8', '3.9', '3.7', 'library', 'docs']
title = 'datetime.strftime("%Y") not consistent for years < 1000'
updated_at = <Date 2022-02-10.19:47:24.483>
user = 'https://github.com/florentx'

bugs.python.org fields:

activity = <Date 2022-02-10.19:47:24.483>
actor = 'jaraco'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2011-10-31.20:12:37.023>
creator = 'flox'
dependencies = []
files = ['23577', '41476', '42136']
hgrepos = []
issue_num = 13305
keywords = ['patch', 'easy']
message_count = 30.0
messages = ['146740', '146743', '146745', '146750', '146751', '146752', '146765', '146767', '146967', '146972', '146976', '146978', '252165', '257271', '257383', '257397', '261577', '261607', '261608', '261609', '261637', '261638', '261639', '261640', '307417', '359735', '359740', '394251', '413015', '413021']
nosy_count = 13.0
nosy_names = ['jaraco', 'belopolsky', 'vstinner', 'ned.deily', 'ezio.melotti', 'flox', 'docs@python', 'python-dev', 'martin.panter', 'Elena.Oat', 'p-ganssle', 'Fronkan', 'cklarson']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = '3173'
type = 'behavior'
url = 'https://bugs.python.org/issue13305'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[florentx]

See msg146725 on bpo-13291.

on linux
>>> datetime(1,  2, 10, 11, 41, 23).strftime("%Y")
'1'

on osx
>>> datetime(1,  2, 10, 11, 41, 23).strftime("%Y")
'0001'


>>> datetime.strptime('0001', '%Y')
datetime.datetime(1, 1, 1, 0, 0)

>>> datetime.strptime('1', '%Y')
ValueError: time data '1' does not match format '%Y'

[florentx]

FWIW, issue bpo-1777412 added support for years < 1000 to Python 3.3 strftime.

[abalkin]

I am not sure this can be fixed without distributing our own implementation of strftime. See bpo-3173.

[florentx]

There's many discrepancies between OS X and Linux about time formatting...

OS X
>>> from datetime import datetime
>>> datetime(1900, 1, 1).strftime("%6Y")
'6Y'

Linux
>>> from datetime import datetime
>>> datetime(1900, 1, 1).strftime("%6Y")
'001900'

BTW, these discrepancies are already mentioned:
http://docs.python.org/dev/library/datetime.html#strftime-strptime-behavior

“The full set of format codes supported varies across platforms, because Python calls the platform C library’s strftime() function, and platform variations are common.”

We should had an asterisk to the "%Y" saying that the padding is not consistent across platforms.

[florentx]

Proposed patch to fix the issue in xmlrpc.client

[python-dev]

New changeset 3f025427f02b by Florent Xicluna in branch 'default':
Fix regression due to changeset 2096158376e5 (issue bpo-13305).
http://hg.python.org/cpython/rev/3f025427f02b

[vstinner]

Le 01/11/2011 00:07, Roundup Robot a écrit :

Roundup Robot<devnull@psf.upfronthosting.co.za> added the comment:

New changeset 3f025427f02b by Florent Xicluna in branch 'default':
Fix regression due to changeset 2096158376e5 (issue bpo-13305).
http://hg.python.org/cpython/rev/3f025427f02b

I don't like this hack. If there is a bug in time.strftime(), we need to
fix time.strftime(), not xmlrpclib.

Is there a test for the hack?

[python-dev]

New changeset 230f0956aaa3 by Florent Xicluna in branch 'default':
Strengthen the tests for format '%Y', in relation with issue bpo-13305.
http://hg.python.org/cpython/rev/230f0956aaa3

[vstinner]

Did your commit fix the issue or not?

[florentx]

I understand that the issue is because the C standard does not specify the length of the string returned by '%Y'.

The changeset 230f0956aaa3 adds a test to verify that either '%Y' or '%4Y' returns a 4-digits value usable to produce ISO-8601 representations.

Now it is a documentation issue: add a comment to the "%Y" specifier saying that the padding is not applicable to all platforms and in such case the "%4Y" specifier should return the 4-digit value.

[vstinner]

Since the changeset 55a3b563f0dbed04af317f632f7f3c0f6abe175b, test_strptime is failing on "AMD64 Gentoo Wide 3.x" buildbot:

======================================================================
FAIL: test_strptime (test.test_time.TimeTestCase)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.ochtman-gentoo-amd64/build/Lib/test/test_time.py", line 159, in test_strptime
    time.strptime(strf_output, format)
ValueError: time data 'LMT' does not match format '%Z'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.ochtman-gentoo-amd64/build/Lib/test/test_time.py", line 162, in test_strptime
    (format, strf_output))
AssertionError: conversion specifier '%Z' failed with 'LMT' input.

---

http://www.python.org/dev/buildbot/all/builders/AMD64%20Gentoo%20Wide%203.x/builds/2661