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Description
Bug report
For example the following program fails with eitherassert WeirdClass.value == 2 orassert WeirdClass.value == 3 in recent Python versions:
importsysclassBase:value=1classMeta(type):defmro(cls):return (cls,Base,object)classWeirdClass(metaclass=Meta):passassertBase.value==1assertWeirdClass.value==1Base.value=2assertBase.value==2assertWeirdClass.value==2Base.value=3assertBase.value==3assertWeirdClass.value==3
Adding intervening calls tosys _clear_internal_caches() makes the test pass.
| Version | Result |
|---|---|
| 3.7 | OK |
| 3.8 | OK |
| 3.9 | OK |
| 3.10 | AssertionError: assert WeirdClass.value == 2 |
| 3.11 | AssertionError: assert WeirdClass.value == 2 |
| 3.12 | AssertionError: assert WeirdClass.value == 2 |
| 3.13 | AssertionError: assert WeirdClass.value == 3 |
| main | AssertionError: assert WeirdClass.value == 3 |
We have code that checks for this case, but it hasn't worked properly in Python 3.10+:
Lines 1107 to 1112 in5c89adf
| staticvoid | |
| type_mro_modified(PyTypeObject*type,PyObject*bases) { | |
| /* | |
| Check that all base classes or elements of the MRO of type are | |
| able to be cached. This function is called after the base | |
| classes or mro of the type are altered. |
We also have a test that partly covers this case, but doesn't detect the bug:
cpython/Lib/test/test_capi/test_type.py
Lines 40 to 66 in5c89adf
| deftest_freeze_meta(self): | |
| """test PyType_Freeze() with overridden MRO""" | |
| type_freeze=_testcapi.type_freeze | |
| classBase: | |
| value=1 | |
| classMeta(type): | |
| defmro(cls): | |
| return (cls,Base,object) | |
| classFreezeThis(metaclass=Meta): | |
| """This has `Base` in the MRO, but not tp_bases""" | |
| self.assertEqual(FreezeThis.value,1) | |
| withself.assertRaises(TypeError): | |
| type_freeze(FreezeThis) | |
| Base.value=2 | |
| self.assertEqual(FreezeThis.value,2) | |
| type_freeze(Base) | |
| withself.assertRaises(TypeError): | |
| Base.value=3 | |
| type_freeze(FreezeThis) | |
| self.assertEqual(FreezeThis.value,2) |