gh-120713: normalize year with century for datetime.strftime

[blhsing]

On some platforms such as Linux, datetime.strftime does not 0-pad a year <= 999 when formatting with '%Y' despite the documentation claiming an example output of "0001, 0002, …". The same issue applies when formatting with "%G".

This PR fixes the issue by formatting a year with century with '%04ld' using sprintf (in C) or '{:04}' using str.format (in Python) if the platform is found to show the aforementioned behavior.

• Issue: datetime.strftime("%Y") is not padding correctly #120713
• Issue: datetime.strftime("%Y") not consistent for years < 1000 #57514

[serhiy-storchaka]

Note that %G also needs a fix.

[blhsing]

Note that %G also needs a fix.

Right. It's now accounted for. The calculation of ISO-8601 year for '%G' isn't straightforward so I'm obtaining it from the C strftime instead.

[serhiy-storchaka]

Thank you for addressing my comments.

I think that this is the right way to fix this problem, but we should still get confirmation from other core developers.

The code is much more complicated now with the support of "%G", and the C code has some bugs.

[blhsing]

Thanks for enduring my nitpicking, and thanks for the PR :)

Thank you so much for taking the time to point me in the right direction!

[miss-islington-app]

Thanks @blhsing for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @blhsing and @serhiy-storchaka, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 6d34938dc8163f4a4bcc68069a1645a7ab76e935 3.12

[bedevere-app]

GH-121144 is a backport of this pull request to the 3.13 branch.

[serhiy-storchaka]

Thank you for your work and patience @blhsing. My apologies for our too picky reviews.

[bedevere-app]

GH-121145 is a backport of this pull request to the 3.12 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Ubuntu NoGIL Refleaks 3.13 has failed when building commit 9f6f879.

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/#builders/1431/builds/335) and take a look at the build logs.
4. Check if the failure is related to this commit (9f6f879) 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/#builders/1431/builds/335

Failed tests:

• test_pickle

Test leaking resources:

• test_pickle: memory blocks
• test_pickle: references

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

==

Click to see traceback logs

remote: Enumerating objects: 10, done.        
remote: Counting objects:  10% (1/10)        
remote: Counting objects:  20% (2/10)        
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remote: Counting objects:  90% (9/10)        
remote: Counting objects: 100% (10/10)        
remote: Counting objects: 100% (10/10), done.        
remote: Compressing objects:  12% (1/8)        
remote: Compressing objects:  25% (2/8)        
remote: Compressing objects:  37% (3/8)        
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remote: Compressing objects:  87% (7/8)        
remote: Compressing objects: 100% (8/8)        
remote: Compressing objects: 100% (8/8), done.        
remote: Total 10 (delta 2), reused 5 (delta 2), pack-reused 0        
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HEAD is now at 9f6f8790ef Revert "[3.13] gh-120713: Normalize year with century for datetime.strftime (GH-120820) (GH-121144)" (GH-122408)
Switched to and reset branch '3.13'

configure: WARNING: no system libmpdecimal found; falling back to bundled libmpdecimal (deprecated and scheduled for removal in Python 3.15)

make: *** [Makefile:2264: buildbottest] Error 2