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gh-135385: Fix memory regression for classes with both __slots__ and __dict__ #135389

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gh-135385: Fix memory regression for classes with both __slots__ and __dict__ #135389

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gh-135385: Fix memory regression for classes with both __slots__ and …
shuimu5418 Jun 11, 2025
7ed3c02
Update Misc/NEWS.d/next/Core_and_Builtins/2025-06-11-21-40-21.gh-issu…
shuimu5418 Jun 11, 2025
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-06-11-21-40-21.gh-issue-135385.e2TFON.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a memory regression for classes that have both :attr:`~object.__slots__` and
:attr:`~object.__dict__`.
14 changes: 13 additions & 1 deletion Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4621,7 +4621,19 @@ type_new_descriptors(const type_new_ctx *ctx, PyTypeObject *type)
}

type->tp_basicsize = slotoffset;
type->tp_itemsize = ctx->base->tp_itemsize;

// Only inherit tp_itemsize if this type defines its own __slots__
// Classes that don't define __slots__ but inherit from __slots__ classes
// should not inherit tp_itemsize as they don't use variable-size items
if (et->ht_slots != NULL && PyTuple_GET_SIZE(et->ht_slots) > 0) {
// This type defines its own __slots__, inherit tp_itemsize
type->tp_itemsize = ctx->base->tp_itemsize;
}
else {
// This type doesn't define __slots__, don't inherit tp_itemsize
type->tp_itemsize = 0;
}

type->tp_members = _PyHeapType_GET_MEMBERS(et);
return 0;
}
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