Add set_freezable() for per-object freeze policy#77
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mjp41 merged 8 commits intoimmutable-mainfrom Mar 6, 2026
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Add set_freezable(obj, status) to control whether individual objects
can be frozen. The status is one of four values:
FREEZABLE_YES - always freezable
FREEZABLE_NO - never freezable
FREEZABLE_EXPLICIT - freezable only when freeze() is called directly
on the object, not when reached as a child
FREEZABLE_PROXY - reserved for future module proxy use
Storage uses a two-tier strategy: first tries setting a __freezable__
attribute on the object (works for any object with a __dict__), falling
back to a weakref-keyed dictionary in the interpreter state (works for
__slots__ objects with __weakref__ support). If neither is possible,
raises TypeError.
During freeze, check_freezable() queries the status by checking the
__freezable__ attribute first, then the weakref dictionary. For
EXPLICIT, the freeze root object is tracked in FreezeState so that
direct vs child freezing can be distinguished.
The old standalone __freezable__ = False check in traverse_freeze is
removed; all __freezable__ handling is now unified through
check_freezable() and _PyImmutability_GetFreezable().
Changes:
- Include/internal/pycore_immutability.h: add _Py_freezable_status
enum, freezable_objects dict, and destroy_objects_cb to state
- Include/cpython/immutability.h: declare SetFreezable/GetFreezable
- Python/immutability.c: implement SetFreezable (attr-first, weakref
fallback), GetFreezable (attr-first, weakref fallback),
_destroy_dict callback, FreezeState.root, updated check_freezable
- Modules/_immutablemodule.c: expose set_freezable() and constants
- Lib/immutable.py: export set_freezable and FREEZABLE_* constants
- Python/pystate.c: cleanup new state fields in interpreter_clear()
- Lib/test/test_freeze/test_set_freezable.py: 18 tests covering all
status values, storage strategies, edge cases, and constants
xFrednet
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Mar 6, 2026
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Some high level nits, but the rest LGTM. Nice work :D
| def test_object_without_weakref_support_raises(self): | ||
| # Built-in ints don't support weak references or attribute setting. | ||
| with self.assertRaises(TypeError): | ||
| set_freezable(42, FREEZABLE_NO) |
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Should we allow setting freezability for shallow immutable objects in the first place?
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Good question, I don't know. There are a bunch of defaults I am not sure on the right choices for.
|
|
||
| // Check is object is subclass of NotFreezable | ||
| // TODO: Would be nice for this to be faster. | ||
| if (PyObject_IsInstance(obj, (PyObject *)&_PyNotFreezable_Type) == 1){ |
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Now we should be able to remove the _PyNotFreezable_Type (Can be done in a follow up.)
Co-authored-by: Fridtjof Stoldt <xFrednet@gmail.com>
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Add
set_freezable(obj, status)to control whether individual objectscan be frozen. The status is one of four values:
FREEZABLE_YES- always freezableFREEZABLE_NO- never freezableFREEZABLE_EXPLICIT- freezable only when freeze() is called directlyon the object, not when reached as a child
FREEZABLE_PROXY- reserved for future module proxy useStorage uses a two-tier strategy: first tries setting a
__freezable__attribute on the object (works for any object with a
__dict__), fallingback to a weakref-keyed dictionary in the interpreter state (works for
__slots__objects with__weakref__support). If neither is possible,raises TypeError.
During freeze,
check_freezable()queries the status by checking the__freezable__attribute first, then the weakref dictionary. ForEXPLICIT, the freeze root object is tracked in
FreezeStateso thatdirect vs child freezing can be distinguished.
The old standalone
__freezable__ = Falsecheck intraverse_freezeisremoved; all
__freezable__handling is now unified throughcheck_freezable()and_PyImmutability_GetFreezable().Changes:
Include/internal/pycore_immutability.h: add_Py_freezable_statusenum,
freezable_objectsdict, anddestroy_objects_cbto stateInclude/cpython/immutability.h: declareSetFreezable/GetFreezablePython/immutability.c: implementSetFreezable(attr-first, weakreffallback),
GetFreezable(attr-first, weakref fallback),_destroy_dictcallback,FreezeState.root, updatedcheck_freezableModules/_immutablemodule.c: exposeset_freezable()and constantsLib/immutable.py: exportset_freezableandFREEZABLE_*constantsPython/pystate.c: cleanup new state fields ininterpreter_clear()Lib/test/test_freeze/test_set_freezable.py: 18 tests covering allstatus values, storage strategies, edge cases, and constants
_blocking_onand_module_locksto use this mechanism.