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[3.15] gh-150868: Fix sum() deallocating a float subclass as an exact float (GH-151063) - #161048
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…float (pythonGH-151063) * pythongh-151060: Fix sum() deallocating a float subclass as an exact float The complex-total fast path in builtin_sum_impl() guarded with PyFloat_Check() (which accepts subclasses) but freed the item with _Py_DECREF_SPECIALIZED(item, _PyFloat_ExactDealloc), which assumes an exact float. A float subclass instance reaching refcount 0 in that loop aborts on an assertion in debug builds, and in release builds skips the subclass tp_dealloc (type refcount leak, __del__ never runs, subclass object pushed onto the float freelist). Use PyFloat_CheckExact() instead, matching the float-total branch, so subclass instances fall through to the generic PyNumber_Add() path. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * pythongh-150868: Also use exact-type checks for ints in the fast sum() loops Per review: use PyLong_CheckExact with the specialized exact-int deallocator in the float and complex fast-sum loops, so int subclasses take the generic path. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> --------- (cherry picked from commit 47c249a) Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This was referenced Oct 31, 2026
skirpichev
approved these changes
Nov 1, 2026
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The complex-total fast path in builtin_sum_impl() guarded with
PyFloat_Check() (which accepts subclasses) but freed the item with
_Py_DECREF_SPECIALIZED(item, _PyFloat_ExactDealloc), which assumes an
exact float. A float subclass instance reaching refcount 0 in that loop
aborts on an assertion in debug builds, and in release builds skips the
subclass tp_dealloc (type refcount leak, del never runs, subclass
object pushed onto the float freelist).
Use PyFloat_CheckExact() instead, matching the float-total branch, so
subclass instances fall through to the generic PyNumber_Add() path.
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com
Per review: use PyLong_CheckExact with the specialized exact-int
deallocator in the float and complex fast-sum loops, so int subclasses
take the generic path.
Co-Authored-By: Claude Fable 5 noreply@anthropic.com
(cherry picked from commit 47c249a)
Co-authored-by: Pieter Eendebak pieter.eendebak@gmail.com
Co-authored-by: Claude Opus 4.8 (1M context) noreply@anthropic.com