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gh-87298: Add tests for find_in_strong_cache() bug in _zoneinfo #24829

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Merged
merged 5 commits into from
Jul 1, 2025
Merged

gh-87298: Add tests for find_in_strong_cache() bug in _zoneinfo #24829

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1f7a1fa
bpo-43132: Add tests for find_in_strong_cache() bug in _zoneinfo
ZackerySpytz Mar 11, 2021
ae1ba75
Merge branch 'main' into bpo-43132-find_in_strong_cache-_zoneinfo-tests
iritkatriel May 14, 2023
41298bd
Merge branch 'main' into bpo-43132-find_in_strong_cache-_zoneinfo-tests
erlend-aasland Jan 5, 2024
7a4accd
Merge branch 'main' into bpo-43132-find_in_strong_cache-_zoneinfo-tests
serhiy-storchaka Jul 1, 2025
446d058
Fix and simplify tests.
serhiy-storchaka Jul 1, 2025
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43 changes: 43 additions & 0 deletions Lib/test/test_zoneinfo/test_zoneinfo.py
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,10 @@ def tearDownModule():
shutil.rmtree(TEMP_DIR)


class CustomError(Exception):
pass


class TzPathUserMixin:
"""
Adds a setUp() and tearDown() to make TZPATH manipulations thread-safe.
Expand Down Expand Up @@ -404,6 +408,25 @@ def test_time_fixed_offset(self):
self.assertEqual(t.utcoffset(), offset.utcoffset)
self.assertEqual(t.dst(), offset.dst)

def test_cache_exception(self):
class Incomparable(str):
eq_called = False
def __eq__(self, other):
self.eq_called = True
raise CustomError
__hash__ = str.__hash__

key = "America/Los_Angeles"
tz1 = self.klass(key)
key = Incomparable(key)
try:
tz2 = self.klass(key)
except CustomError:
self.assertTrue(key.eq_called)
else:
self.assertFalse(key.eq_called)
self.assertIs(tz2, tz1)


class CZoneInfoTest(ZoneInfoTest):
module = c_zoneinfo
Expand Down Expand Up @@ -1507,6 +1530,26 @@ def test_clear_cache_two_keys(self):
self.assertIsNot(dub0, dub1)
self.assertIs(tok0, tok1)

def test_clear_cache_refleak(self):
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Apparently I wrote this function 4 years ago, but coming back to it now it is opaque as heck, so we should probably describe what this test is about.

Suggested change
def test_clear_cache_refleak(self):
def test_clear_cache_refleak(self):
# bpo-43132: The portion of the C implementation of ZoneInfo that
# ejects specific keys from the strong cache (i.e. the LRU cache) was
# leaking references if comparing to the key object failed; because the
# strong cache is not currently implemented for subclasses, this test
# only really applies to the C implementation of the ZoneInfo class.

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We may also want to skip this test if self.klass is not exactly the C implementation of ZoneInfo, since otherwise it's a no-op.

class Stringy(str):
allow_comparisons = True
def __eq__(self, other):
if not self.allow_comparisons:
raise CustomError
return super().__eq__(other)
__hash__ = str.__hash__

key = Stringy("America/Los_Angeles")
self.klass(key)
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To increase the chance that this actually works:

Suggested change
self.klass(key)
self.klass.clear_cache(only_keys="America/Los_Angeles")
self.klass(key)

key.allow_comparisons = False
try:
# Note: This is try/except rather than assertRaises because
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I realize that I wrote this function, but it kind of bothers me that this can silently become a no-op (and in fact this is silently a no-op for all subclasses ZoneInfo). I think that the only way around it is fairly annoying if we want to allow tests to run in parallel, which is that we would need to acquire a lock around anything that deals with the cache.

# there is no guarantee that the key is even still in the cache,
# or that the key for the cache is the original `key` object.
self.klass.clear_cache(only_keys="America/Los_Angeles")
except CustomError:
pass


class CZoneInfoCacheTest(ZoneInfoCacheTest):
module = c_zoneinfo
Expand Down
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