https://github.com/python/cpython/commit/b12497756ba0242a2a389dd1bb6fb26ddbd48602
commit: b12497756ba0242a2a389dd1bb6fb26ddbd48602
branch: main
author: Pengyu Lee <[email protected]>
committer: vsajip <[email protected]>
date: 2026-10-20T16:24:13+01:00
summary:
gh-159690: Fix timed log rotation after a failed or duplicate rollover
(GH-159692)
files:
A Misc/NEWS.d/next/Library/2026-10-20-00-12-05.gh-issue-159690.vZgLP6.rst
M Lib/logging/handlers.py
M Lib/test/test_logging.py
diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index e225a21da408fad..9d31cd4bc3a1018 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -469,6 +469,7 @@ def doRollover(self):
timeTuple = time.localtime(t + addend)
dfn = self.rotation_filename(self.baseFilename + "." +
time.strftime(self.suffix, timeTuple))
+ self.rolloverAt = self.computeRollover(currentTime)
if os.path.exists(dfn):
# Already rolled over.
return
@@ -482,7 +483,6 @@ def doRollover(self):
os.remove(s)
if not self.delay:
self.stream = self._open()
- self.rolloverAt = self.computeRollover(currentTime)
class WatchedFileHandler(logging.FileHandler):
"""
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index b1852ee43b594fa..0ab1f7ef31afb17 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -6902,6 +6902,75 @@ def test_rollover_at_midnight(self, weekly=False):
def test_rollover_at_weekday(self):
self.test_rollover_at_midnight(weekly=True)
+ def _make_fake_time_handler(self, now, when='S', **kwargs):
+ dirname = tempfile.mkdtemp()
+ self.addCleanup(os_helper.rmtree, dirname)
+ fn = os.path.join(dirname, 'test.log')
+ with patch('time.time', lambda: now[0]):
+ fh = logging.handlers.TimedRotatingFileHandler(
+ fn, when=when, encoding='utf-8', delay=True, **kwargs)
+ self.addCleanup(fh.close)
+ return fh
+
+ def test_rollover_after_failed_rollover(self):
+ for target in 'os.remove', '_open':
+ with self.subTest(target=target):
+ now = [1_000_000_000]
+ fh = self._make_fake_time_handler(now, backupCount=1)
+ fn = fh.baseFilename
+ emit = lambda msg: fh.emit(logging.makeLogRecord({'msg': msg}))
+ with patch('time.time', lambda: now[0]):
+ for msg in 'a', 'b':
+ now[0] += 2
+ emit(msg)
+ now[0] += 2
+ if target == '_open':
+ failure = patch.object(fh, '_open',
side_effect=OSError)
+ fh.delay = False
+ else:
+ failure = patch('os.remove', side_effect=OSError)
+ with failure as failed, support.captured_stderr():
+ emit('c')
+ failed.assert_called_once()
+ self.assertGreater(fh.rolloverAt, now[0])
+ fh.delay = True
+ for msg in 'd', 'e':
+ now[0] += 2
+ emit(msg)
+ fh.close()
+ with open(fn, encoding='utf-8') as f:
+ self.assertEqual(f.read(), 'e\n')
+ backups = [f for f in os.listdir(os.path.dirname(fn))
+ if f != 'test.log']
+ self.assertEqual(len(backups), 1)
+
+ def test_rollover_existing_backup(self):
+ now = [1_000_000_000]
+ fh = self._make_fake_time_handler(now)
+ fn = fh.baseFilename
+ with patch('time.time', lambda: now[0]):
+ fh.emit(logging.makeLogRecord({'msg': 'a'}))
+ t = fh.rolloverAt - fh.interval
+ dfn = fh.rotation_filename(
+ fn + '.' + time.strftime(fh.suffix, time.localtime(t)))
+ with open(dfn, 'w', encoding='utf-8') as f:
+ f.write('existing\n')
+ now[0] += 2
+ fh.emit(logging.makeLogRecord({'msg': 'b'}))
+ self.assertGreater(fh.rolloverAt, now[0])
+ t = fh.rolloverAt - fh.interval
+ next_dfn = fh.rotation_filename(
+ fn + '.' + time.strftime(fh.suffix, time.localtime(t)))
+ now[0] += 2
+ fh.emit(logging.makeLogRecord({'msg': 'c'}))
+ fh.close()
+ with open(dfn, encoding='utf-8') as f:
+ self.assertEqual(f.read(), 'existing\n')
+ with open(next_dfn, encoding='utf-8') as f:
+ self.assertEqual(f.read(), 'a\nb\n')
+ with open(fn, encoding='utf-8') as f:
+ self.assertEqual(f.read(), 'c\n')
+
def test_invalid(self):
assertRaises = self.assertRaises
assertRaises(ValueError, logging.handlers.TimedRotatingFileHandler,
diff --git
a/Misc/NEWS.d/next/Library/2026-10-20-00-12-05.gh-issue-159690.vZgLP6.rst
b/Misc/NEWS.d/next/Library/2026-10-20-00-12-05.gh-issue-159690.vZgLP6.rst
new file mode 100644
index 000000000000000..b94d79501b9abed
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-10-20-00-12-05.gh-issue-159690.vZgLP6.rst
@@ -0,0 +1,3 @@
+Fix :class:`logging.handlers.TimedRotatingFileHandler` permanently stopping
+rollover after a rollover failed or its backup file already existed, for
+example at a DST change.
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