gh-69142: add %:z strftime format code

[ThomasWaldmann]

datetime.isoformat generates the tzoffset with colons, but there
was no format code to make strftime output the same format.

for simplicity and consistency the %:z formatting behaves mostly
as %z, with the exception of adding colons. this includes the
dynamic behaviour of adding seconds and microseconds only when
needed (when not 0).

this fixes the still open "generate" part of this issue:

#69142

• Issue: No way to generate or parse timezone as produced by datetime.isoformat() #69142

[bedevere-bot]

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[cpython-cla-bot]

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[gvanrossum]

Very elegant, and the code LGTM. But would you be so kind as to add a few unit tests?

[ThomasWaldmann]

@gvanrossum thanks. i even tried to start with unit tests, but it looked hard to fit in the existing test code.

but i'll try again... :-)

[merwok]

Here are the tests for %Z: https://github.com/python/cpython/blob/main/Lib/test/datetimetester.py#L1453

You could add another method, create the datetime instances that you need, then compare method calls with expected outputs.

[ThomasWaldmann]

@merwok thanks.

@gvanrossum first attempt was very elegant / short, but incorrect:

• pin pointer was not advanced correctly for naive datetime
• code needs 2 different replacement variables for %z and %:z (otherwise output is wrong if both formats are used in the same format string)

[gvanrossum]

I haven't tried to look into why the tests still fail. You know you can run tests locally right?

Also, please don't force-push (which I think you've done) once the review is under way. We'll squash-merge in the end anyway.

[merwok]

Please avoid force pushes for Python PRs: https://devguide.python.org/getting-started/pull-request-lifecycle/index.html

[ThomasWaldmann]

Of course I ran the tests locally before pushing (but maybe in an unusual way), so there is this interesting finding (on macOS 12, in case it matters):

% ./python.exe Lib/test/datetimetester.py -v  # all works (including the test fails seen in next command)
% ./python.exe -m test -v test_datetime # test_datetime fails

[gvanrossum]

There seems to be still something failing. Do you need help figuring that out?

[ThomasWaldmann]

@gvanrossum yes, i could not find the cause for the strange behaviour yet.

Update:

Looks like _Fast tests are ok vs _Pure tests are broken.

Ah, just found Lib/datetime.py is the pure python implementation that also needs adapting.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @merwok for commit 8f29d9d 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[ThomasWaldmann]

That patchcheck automation is not very helpful. It does not show errors, nor line numbers, just recommends to run make patchcheck locally, which is broken for me:

tw@mba2020 cpython % make patchcheck
Checked 109 modules (30 built-in, 77 shared, 2 n/a on macosx-12.5-arm64, 0 disabled, 0 missing, 0 failed on import)
./python.exe ./Tools/scripts/patchcheck.py
Enter passphrase for key '...': 
upstream/main
Getting the list of files that have been added/changed ... fatal: ambiguous argument 'upstream/main': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
error running git diff --name-status upstream/main
make: *** [patchcheck] Error 1

[merwok]

it works for me, and I do have the recommended setup with an upstream origin for this repo (origin being my fork)

[gvanrossum]

Getting very close. I have some nits to pick about the docs.

@kumaraditya303 Have you reviewed datetime.py and is it to your liking?

[kumaraditya303]

Have you reviewed datetime.py and is it to your liking?

LGTM

[gvanrossum]

Yes! I'll merge. Thanks TW for the PR and thanks Kumar for all the review work you did.

[ThomasWaldmann]

BTW, will we have to wait some years for this until 3.12 becomes minimum requirement or can this go into older pythons also?

[gvanrossum]

BTW, will we have to wait some years for this until 3.12 becomes minimum requirement or can this go into older pythons also?

Alas, this looks like a new feature to me so it won't be backported.

[ThomasWaldmann]

OK, pity. OTOH, even if it were backported, it would only go into 3.11.latest, so would not help if somebody has 3.11.lessthanthat.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x Debian 3.x has failed when building commit 023c51d.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/49/builds/3543) and take a look at the build logs.
4. Check if the failure is related to this commit (023c51d) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/49/builds/3543

Failed tests:

• test_multiprocessing_forkserver

Summary of the results of the build (if available):

== Tests result: FAILURE then ENV CHANGED ==

420 tests OK.

10 slowest tests:

• test_concurrent_futures: 2 min 27 sec
• test_tools: 2 min 17 sec
• test_multiprocessing_spawn: 1 min 58 sec
• test_tokenize: 1 min 24 sec
• test_asyncio: 1 min 19 sec
• test_gdb: 1 min 12 sec
• test_multiprocessing_fork: 1 min 10 sec
• test_signal: 1 min 10 sec
• test_capi: 1 min 6 sec
• test_unparse: 41.5 sec

1 test altered the execution environment:
test_asyncio

14 tests skipped:
test_dbm_ndbm test_devpoll test_ioctl test_kqueue test_launcher
test_msilib test_startfile test_tix test_tkinter test_ttk
test_winconsoleio test_winreg test_winsound test_zipfile64

1 re-run test:
test_multiprocessing_forkserver

Total duration: 19 min 40 sec

Click to see traceback logs

remote: Enumerating objects: 16, done.        
remote: Counting objects:   6% (1/15)        
remote: Counting objects:  13% (2/15)        
remote: Counting objects:  20% (3/15)        
remote: Counting objects:  26% (4/15)        
remote: Counting objects:  33% (5/15)        
remote: Counting objects:  40% (6/15)        
remote: Counting objects:  46% (7/15)        
remote: Counting objects:  53% (8/15)        
remote: Counting objects:  60% (9/15)        
remote: Counting objects:  66% (10/15)        
remote: Counting objects:  73% (11/15)        
remote: Counting objects:  80% (12/15)        
remote: Counting objects:  86% (13/15)        
remote: Counting objects:  93% (14/15)        
remote: Counting objects: 100% (15/15)        
remote: Counting objects: 100% (15/15), done.        
remote: Compressing objects:   7% (1/13)        
remote: Compressing objects:  15% (2/13)        
remote: Compressing objects:  23% (3/13)        
remote: Compressing objects:  30% (4/13)        
remote: Compressing objects:  38% (5/13)        
remote: Compressing objects:  46% (6/13)        
remote: Compressing objects:  53% (7/13)        
remote: Compressing objects:  61% (8/13)        
remote: Compressing objects:  69% (9/13)        
remote: Compressing objects:  76% (10/13)        
remote: Compressing objects:  84% (11/13)        
remote: Compressing objects:  92% (12/13)        
remote: Compressing objects: 100% (13/13)        
remote: Compressing objects: 100% (13/13), done.        
remote: Total 16 (delta 2), reused 3 (delta 2), pack-reused 1        
From https://github.com/python/cpython
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HEAD is now at 023c51d9d8 gh-69142: add %:z strftime format code (gh-95983)
Switched to and reset branch 'main'

make: *** [Makefile:1865: buildbottest] Error 3

[gvanrossum]

I don't see how this change could break test_multiprocessing_forkserver. From the logs it appears that the first time this test ran it exceeded the 15 minute time limit. The second time it ran fine. Let's ignore this unless the buildbot police get involved.