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Commitd764eb6

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JelleZijlstrancoghlanencukouserhiy-storchaka
authored andcommitted
gh-135228: When@DataClass(slots=True) replaces a dataclass, make the original class collectible (take 2) (GH-137047)
Remove the `__dict__` and `__weakref__` descriptors from the original class when creating a dataclass from it.An interesting hack, but more localized in scope thangh-135230.This may be a breaking change if people intentionally keep the original class aroundwhen using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on theoriginal class.(cherry picked from commit6859b95)Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>Co-authored-by: Petr Viktorin <encukou@gmail.com>Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
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5 files changed

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5 files changed

+117
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lines changed

‎Lib/dataclasses.py‎

Lines changed: 4 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1283,6 +1283,10 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
12831283
if'__slots__'incls.__dict__:
12841284
raiseTypeError(f'{cls.__name__} already specifies __slots__')
12851285

1286+
# gh-102069: Remove existing __weakref__ descriptor.
1287+
# gh-135228: Make sure the original class can be garbage collected.
1288+
sys._clear_type_descriptors(cls)
1289+
12861290
# Create a new dict for our new class.
12871291
cls_dict=dict(cls.__dict__)
12881292
field_names=tuple(f.nameforfinfields(cls))
@@ -1300,12 +1304,6 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
13001304
# available in _MARKER.
13011305
cls_dict.pop(field_name,None)
13021306

1303-
# Remove __dict__ itself.
1304-
cls_dict.pop('__dict__',None)
1305-
1306-
# Clear existing `__weakref__` descriptor, it belongs to a previous type:
1307-
cls_dict.pop('__weakref__',None)# gh-102069
1308-
13091307
# And finally create the class.
13101308
qualname=getattr(cls,'__qualname__',None)
13111309
newcls=type(cls)(cls.__name__,cls.__bases__,cls_dict)

‎Lib/test/test_dataclasses/__init__.py‎

Lines changed: 35 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3804,6 +3804,41 @@ class WithCorrectSuper(CorrectSuper):
38043804
# that we create internally.
38053805
self.assertEqual(CorrectSuper.args, ["default","default"])
38063806

3807+
deftest_original_class_is_gced(self):
3808+
# gh-135228: Make sure when we replace the class with slots=True, the original class
3809+
# gets garbage collected.
3810+
defmake_simple():
3811+
@dataclass(slots=True)
3812+
classSlotsTest:
3813+
pass
3814+
3815+
returnSlotsTest
3816+
3817+
defmake_with_annotations():
3818+
@dataclass(slots=True)
3819+
classSlotsTest:
3820+
x:int
3821+
3822+
returnSlotsTest
3823+
3824+
defmake_with_annotations_and_method():
3825+
@dataclass(slots=True)
3826+
classSlotsTest:
3827+
x:int
3828+
3829+
defmethod(self)->int:
3830+
returnself.x
3831+
3832+
returnSlotsTest
3833+
3834+
formakein (make_simple,make_with_annotations,make_with_annotations_and_method):
3835+
withself.subTest(make=make):
3836+
C=make()
3837+
support.gc_collect()
3838+
candidates= [clsforclsinobject.__subclasses__()ifcls.__name__=='SlotsTest'
3839+
andcls.__firstlineno__==make.__code__.co_firstlineno+1]
3840+
self.assertEqual(candidates, [C])
3841+
38073842

38083843
classTestDescriptors(unittest.TestCase):
38093844
deftest_set_name(self):
Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,4 @@
1+
When:mod:`dataclasses` replaces a class with a slotted dataclass, the
2+
original class can now be garbage collected again. Earlier changes in Python
3+
3.14 caused this class to always remain in existence together with the replacement
4+
class synthesized by:mod:`dataclasses`.

‎Python/clinic/sysmodule.c.h‎

Lines changed: 32 additions & 1 deletion
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‎Python/sysmodule.c‎

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2640,6 +2640,47 @@ sys__baserepl_impl(PyObject *module)
26402640
Py_RETURN_NONE;
26412641
}
26422642

2643+
/*[clinic input]
2644+
sys._clear_type_descriptors
2645+
2646+
type: object(subclass_of='&PyType_Type')
2647+
/
2648+
2649+
Private function for clearing certain descriptors from a type's dictionary.
2650+
2651+
See gh-135228 for context.
2652+
[clinic start generated code]*/
2653+
2654+
staticPyObject*
2655+
sys__clear_type_descriptors_impl(PyObject*module,PyObject*type)
2656+
/*[clinic end generated code: output=5ad17851b762b6d9 input=dc536c97fde07251]*/
2657+
{
2658+
PyTypeObject*typeobj= (PyTypeObject*)type;
2659+
if (_PyType_HasFeature(typeobj,Py_TPFLAGS_IMMUTABLETYPE)) {
2660+
PyErr_SetString(PyExc_TypeError,"argument is immutable");
2661+
returnNULL;
2662+
}
2663+
PyObject*dict=_PyType_GetDict(typeobj);
2664+
PyObject*dunder_dict=NULL;
2665+
if (PyDict_Pop(dict,&_Py_ID(__dict__),&dunder_dict)<0) {
2666+
returnNULL;
2667+
}
2668+
PyObject*dunder_weakref=NULL;
2669+
if (PyDict_Pop(dict,&_Py_ID(__weakref__),&dunder_weakref)<0) {
2670+
PyType_Modified(typeobj);
2671+
Py_XDECREF(dunder_dict);
2672+
returnNULL;
2673+
}
2674+
PyType_Modified(typeobj);
2675+
// We try to hold onto a reference to these until after we call
2676+
// PyType_Modified(), in case their deallocation triggers somer user code
2677+
// that tries to do something to the type.
2678+
Py_XDECREF(dunder_dict);
2679+
Py_XDECREF(dunder_weakref);
2680+
Py_RETURN_NONE;
2681+
}
2682+
2683+
26432684
/*[clinic input]
26442685
sys._is_gil_enabled -> bool
26452686
@@ -2836,6 +2877,7 @@ static PyMethodDef sys_methods[] = {
28362877
SYS__STATS_DUMP_METHODDEF
28372878
#endif
28382879
SYS__GET_CPU_COUNT_CONFIG_METHODDEF
2880+
SYS__CLEAR_TYPE_DESCRIPTORS_METHODDEF
28392881
SYS__IS_GIL_ENABLED_METHODDEF
28402882
SYS__DUMP_TRACELETS_METHODDEF
28412883
{NULL,NULL}// sentinel

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