Negative timestamp failure during DST on Windows #145731
Description
Bug report
Bug description:
The AMD64 Windows10 3.x buildbot has started failing:
======================================================================
FAIL: test_fromtimestamp_low_fold_detection (test.datetimetester.TestLocalTimeDisambiguation_Fast.test_fromtimestamp_low_fold_detection)
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Traceback (most recent call last):
File "D:\buildarea\3.x.bolen-windows10\build\Lib\test\datetimetester.py", line 6431, in test_fromtimestamp_low_fold_detection
self.assertEqual(datetime.fromtimestamp(0).fold, 0)
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 1 != 0======================================================================
FAIL: test_mktime (test.test_time.TimeTestCase.test_mktime)
----------------------------------------------------------------------
Traceback (most recent call last):
File "D:\buildarea\3.x.bolen-windows10\build\Lib\test\test_time.py", line 542, in test_mktime
self.assertEqual(t1, t)
~~~~~~~~~~~~~~~~^^^^^^^
AssertionError: 3598.0 != -2
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Ran 64 tests in 3.432s- Last pass: Sat 7th March https://buildbot.python.org/#/builders/146/builds/13306
- First fail: Mon 9th March https://buildbot.python.org/#/builders/146/builds/13307
The US switched to DST on Sunday 8th March.
Only this Windows buildbot fails, it's on EST/EDT:
Last pass:
datetime.datetime.now: 2026-03-07 09:09:35(local)time.time: 1772892576→ 2026-03-07 14:09:36 UTC- Offset: 5 hours → UTC-5 → EST
First fail:
datetime.datetime.now: 2026-03-08 23:01:25(local)time.time: 1773025286→ 2026-03-09 03:01:26 UTC- Offset: 4 hours → UTC-4 → EDT
GitHub Actions is on UTC, so it passes.
Bug likely introduced by #143463, merged in January during standard time, so the tests passed.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Windows