gh-124529: Fix `_strptime` to make `%c`/`%x` accept a year with fewer digits#124778

zuo · 2024-09-30T02:19:20Z

_strptime.TimeRE has been modified, regarding the %c and %x format
codes, to make datetime.datetime.strptime(), datetime.date.strptime()
and time.strptime() accept inputs that contain year numbers consisting
of fewer digits than usual, i.e., not zero-padded to the usual width
of 2 or 4 (which is appropriate for the format code and current locale).

Thanks to that, now the desired behavior described in gh-124529 should be
consistently observed; certain strftime/strptime round trips (involving
%c/%x and small year numbers) no longer raise ValueError for some
platforms/locales (in particular, this was the case on Linux, for various
locales, including C/C.UTF-8).

…igits

rruuaanng · 2024-09-30T06:36:23Z

Misc/NEWS.d/next/Library/2024-09-30-04-49-22.gh-issue-124529.hDDlMH.rst

@@ -0,0 +1,9 @@
+Fix :meth:`datetime.datetime.strptime`, :meth:`datetime.date.strptime` as
+well as :func:`time.strptime` (by modifying :class:`_strptime.TimeRE`) to


Maybe you shouldn't write classes or methods with underscores to NEWS, because they're not public.
And, Maybe you can try to shorten the description of NEWS, it's too long.

OK, shortened the text and removed the reference to a non-public API. :)

rruuaanng · 2024-10-01T01:52:18Z

Misc/NEWS.d/next/Library/2024-09-30-04-49-22.gh-issue-124529.hDDlMH.rst

-``dt.year`` less than 1000) no longer raise ``ValueError`` for some
-locales/platforms (this was the case, e.g., on Linux -- for various
-locales, including ``C``/``C.UTF-8``).
+Fix :meth:`datetime.datetime.strptime`, :meth:`datetime.date.strptime`


I think you should write this
Fixed ``%c``/``%x`` in :meth:`datetime.datetime.strptime`, :meth:`datetime.date.strptime` and :func:`time.strptime` to accept years with fewer digits than the usual 4 or 2 (not zero-padded).
This will be more concise and intuitive.

OK, I've shortened it; yet I'd prefer to keep the information that the fix prevents the error for certain cases of a strftime/strptime round trip (this is the key element of the gh-124529 issue's description).

zuo · 2024-10-01T12:50:26Z

PS Note that the changes concern only the %c/%x-parsing-related behavior, and nothing changes when it comes to %y, %Y and %G (and any non-standard year-representation-related format codes).

zuo · 2024-10-01T12:51:21Z

PPS I added (obviously) the necessary tests (directly related to the changes), but also some indirectly-related ones (especially confirming the unchanged behavior for %y/%Y/%G).

PPPS A suitable mention in the docs has also been added.

zuo · 2024-10-01T14:40:42Z

~~I hope it's ready.~~ [EDIT: not yet]

zuo · 2024-10-01T22:25:42Z

OK, I hope now it's ready. :)

rruuaanng · 2024-10-01T02:50:26Z

Misc/NEWS.d/next/Library/2024-09-30-04-49-22.gh-issue-124529.hDDlMH.rst

+and :func:`time.strptime` to make ``%c`` and ``%x`` accept year numbers
+with fewer digits than the usual 4 or 2 (not zero-padded). This prevents
+:exc:`ValueError` in certain cases of ``strftime/strptime`` round trips.
+Patch by Jan Kaliszewski.


Maybe you should remove the author, because this PR will not be deleted after merging.

Isn't adding such information a common and documented practice?

In the user-oriented update record, users do not care who implemented it.

Most users don't care, indeed; but for authors the presence of such information is a symbolic reward for the contribution. I find this custom nice.
And anyway, as I wrote above, we are talking about a common practice. I am not the right person to ask about changing established practices regarding Python development. :)

rruuaanng · 2024-10-01T23:49:29Z

Lib/test/test_strptime.py

+ ('y', ('9', '100', 'ni')),
+ ('Y', ('7', '42', '999', '10000', 'SPAM')),
+ ):
+fmt="%"+directive


Maybe you can use f-string.

Both ways are valid; the one I chose is more consistent with the existing code in this module.

zuo · 2024-10-04T01:43:57Z

TODO: if this PR's approach is accepted at all, it would be good to adjust it to the changes from PR #124946 (after it is merged).

rruuaanng · 2024-10-11T09:30:11Z

Lib/test/test_strptime.py

+self.fail(str(exc))
+
+try:
+output_year=_strptime._strptime(input_string, fmt)[0][0]


Is't possible for _strptime._strptime to return a one-dim list?

It always returns a 3-tuple, the 0th item of which is a 9-tuple, the 0th item of which is a int representing the year number.

rruuaanng · 2024-10-11T09:30:23Z

Lib/test/test_strptime.py

+fmt="%"+directive
+
+try:
+ (input_string,


Hmmm, Wouldn't this be weird?

Why? IMHO, OK.

donbarbos · 2025-02-27T19:54:50Z

looks like good idea and important fix :)
@zuo are you ready to continue?

zuo · 2025-03-03T02:47:19Z

looks like good idea and important fix :) @zuo are you ready to continue?

Yes, I am :)

Yet I'm not sure what is the next step...

donbarbos · 2025-03-03T02:59:22Z

Doc/library/datetime.rst

 example, "month/day/year" versus "day/month/year"), and the output may
 contain non-ASCII characters.

+ .. versionchanged:: 3.14


as far as i know we use next construction
Suggested change
.. versionchanged:: 3.14
.. versionchanged:: next

and I think you could mark many comments and suggestions as resolved, otherwise they can get in the way of reading and seem ignored :)

and I think you could mark many comments and suggestions as resolved, otherwise they can get in the way of reading and seem ignored :)
Shouldn't it be done by the reviewer who asked a question?

I think you can mark as solved.
at least I can't see this button as the author of suggestion,
so I think only you can close them, especially if there are no plans to continue this topic

zuo requested review from abalkin and pganssle as code owners September 30, 2024 02:19

bedevere-appbot added the awaiting review label Sep 30, 2024

bedevere-appbot mentioned this pull request Sep 30, 2024
datetime.strptime(dt.strftime("%c"), "%c")) fails when year is <1000. #124529
Open

zuo force-pushed the strptime-c-and-y-fix branch from 33d5109 to d3ae17bCompare September 30, 2024 02:51

zuo changed the title ~~gh-124529: Fix _strptime to make %c/%y accept a year with fewer digits~~gh-124529: Fix _strptime to make %c/%x accept a year with fewer digitsSep 30, 2024

pythongh-124529: Fix _strptime to make %c/%x accept year with fewer d…
827db45
…igits

zuo force-pushed the strptime-c-and-y-fix branch from d3ae17b to 91b6bcaCompare September 30, 2024 02:52

Add the blurb
1d916a0

zuo force-pushed the strptime-c-and-y-fix branch from 91b6bca to 1d916a0Compare September 30, 2024 02:54

rruuaanng reviewed Sep 30, 2024
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zuo added 2 commits September 30, 2024 16:29

Fix/improve (and shorten) the blurb
a4ba3c9

Fix/improve/refactor tests and restrict their scope
cef0722

zuo requested a review from rruuaanng September 30, 2024 19:01

zuo added 2 commits September 30, 2024 21:06

Test fail message fixes
6556bdf

Continue enhancing/improving tests
56c84dc

zuo force-pushed the strptime-c-and-y-fix branch from bce4b6d to 56c84dcCompare September 30, 2024 20:44

zuo added 5 commits September 30, 2024 22:58

Improve docstring
b42783c

Add a suitable mention in the docs + improve blurb
97b523e

Docstring edit
6c2addf

Edit the mention in the docs
fb32c03

Minor docs edit
722efe4

rruuaanng reviewed Oct 1, 2024
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zuo added 2 commits October 1, 2024 04:29

Fix/improve tests
7b46a48

Shorten blurb again
3d4116a

zuo requested a review from rruuaanng October 1, 2024 13:23

zuo added 2 commits October 1, 2024 16:09

Minor docs edit
8eac106

Docstring edit
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zuo added 2 commits October 1, 2024 16:35

Docs edit
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Docstring edit
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zuo added 2 commits October 1, 2024 22:32

Minor test improvements/refactoring
949e66a

Add time.strptime()-dedicated test
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zuo force-pushed the strptime-c-and-y-fix branch from c16b5e3 to 059d4c5Compare October 1, 2024 20:33

zuo added 4 commits October 1, 2024 22:42

Minor test improvements/refactoring
95753ac

Merge branch 'main' into strptime-c-and-y-fix
ed4582b

Minor test improvement
990b075

Test improvements/refactoring
ecc359d

zuo added 2 commits October 2, 2024 00:28

Minor refactoring
6d690ca

Merge branch 'main' into strptime-c-and-y-fix
4ad1062

rruuaanng reviewed Oct 1, 2024
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zuo requested a review from rruuaanng October 11, 2024 05:10

rruuaanng reviewed Oct 11, 2024
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zuo requested a review from rruuaanng March 3, 2025 02:46

donbarbos reviewed Mar 3, 2025
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		@@ -0,0 +1,9 @@
		Fix :meth:`datetime.datetime.strptime`, :meth:`datetime.date.strptime` as
		well as :func:`time.strptime` (by modifying :class:`_strptime.TimeRE`) to

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gh-124529: Fix `_strptime` to make `%c`/`%x` accept a year with fewer digits#124778

gh-124529: Fix `_strptime` to make `%c`/`%x` accept a year with fewer digits #124778

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