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gh-155742: Check singletons consistencty in the garbage collector #155801

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gh-155742: Check singletons consistencty in the garbage collector #155801

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48b2e54
gh-155742: Check singletons consistencty in the garbage collector
vstinner Aug 14, 2026
0608d2b
Add support.built_with_c_assertions()
vstinner Aug 14, 2026
c8dd591
Py_DEBUG is already declared in test.support
vstinner Aug 14, 2026
962ef4a
Test more singletons
vstinner Aug 14, 2026
a639176
Remove unused variable (interp)
vstinner Aug 14, 2026
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Add support.built_with_c_assertions() 
Fix also a compiler warning on Windows:

    Objects\object.c(3629,39): warning C4244: 'function': conversion
    from 'long' to 'un signed char', possible loss of data
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@vstinner
vstinner committed Aug 14, 2026
commit 0608d2bbef09dd4be8b0354e246d215ebbadc3c0
10 changes: 2 additions & 8 deletions Lib/test/pythoninfo.py
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Expand Up @@ -611,14 +611,6 @@ def collect_sysconfig(info_add):
value = normalize_text(value)
info_add('sysconfig[%s]' % name, value)

PY_CFLAGS = sysconfig.get_config_var('PY_CFLAGS')
NDEBUG = (PY_CFLAGS and '-DNDEBUG' in PY_CFLAGS)
if NDEBUG:
text = 'ignore assertions (macro defined)'
else:
text= 'build assertions (macro not defined)'
info_add('build.NDEBUG',text)

for name in (
'WITH_DOC_STRINGS',
'WITH_DTRACE',
Expand Down Expand Up @@ -844,6 +836,8 @@ def collect_support(info_add):
support.check_sanitizer(memory=True))
info_add('support.check_sanitizer(ub=True)',
support.check_sanitizer(ub=True))
info_add('support.built_with_c_assertions',
support.built_with_c_assertions())


def collect_support_os_helper(info_add):
Expand Down
11 changes: 11 additions & 0 deletions Lib/test/support/__init__.py
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Expand Up @@ -3492,3 +3492,14 @@ def check_immutable_type(testcase, type):
else:
flags = type_getflags(type)
testcase.assertTrue(flags & Py_TPFLAGS_IMMUTABLETYPE)


def built_with_c_assertions():
# Check if Python was built in debug mode or using --with-assertions
if MS_WINDOWS:
Py_DEBUG = hasattr(sys, 'gettotalrefcount')
return Py_DEBUG

PY_CFLAGS = sysconfig.get_config_var('PY_CFLAGS')
NDEBUG = (PY_CFLAGS and '-DNDEBUG' in PY_CFLAGS)
return (not NDEBUG)
3 changes: 3 additions & 0 deletions Lib/test/test_capi/test_misc.py
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Expand Up @@ -3094,6 +3094,9 @@ def test_ceval_decref(self):
self.assertEqual(lines.count("DESTROY list"), 2)


# _Py_CheckSingletons() is only built if the NDEBUG macro is not defined
@unittest.skipUnless(support.built_with_c_assertions(),
'Python built without C assertions')
class TestCheckSingleton(unittest.TestCase):
# Test _Py_CheckSingletons() which is called by gc.collect()
#
Expand Down
2 changes: 1 addition & 1 deletion Objects/object.c
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Expand Up @@ -3626,7 +3626,7 @@ _Py_CheckSingletons(void)

for (ival=0; ival <= 255; ival++) {
obj = (PyObject*)&_Py_SINGLETON(bytes_characters)[ival];
check_singleton_bytes(obj, 1, ival);
check_singleton_bytes(obj, 1, (unsigned char)ival);
}

// Empty Unicode string ('')
Expand Down
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