https://hg.python.org/cpython/rev/c0d25de5919e changeset: 94397:c0d25de5919e user: Benjamin Peterson <benjamin@python.org> date: Fri Jan 30 13:33:42 2015 -0500 summary: allow changing __class__ between a heaptype and non-heaptype in some cases (closes #22986) Patch by Nathaniel Smith. files: Lib/test/test_descr.py | 16 +++++++ Misc/NEWS | 3 + Objects/typeobject.c | 65 +++++++++++++++++------------ 3 files changed, 57 insertions(+), 27 deletions(-) diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py --- a/Lib/test/test_descr.py +++ b/Lib/test/test_descr.py @@ -1026,6 +1026,22 @@ self.assertEqual(x.foo, 1) self.assertEqual(x.__dict__, {'foo': 1}) + def test_object_class_assignment_between_heaptypes_and_nonheaptypes(self): + class SubType(types.ModuleType): + a = 1 + + m = types.ModuleType("m") + self.assertTrue(m.__class__ is types.ModuleType) + self.assertFalse(hasattr(m, "a")) + + m.__class__ = SubType + self.assertTrue(m.__class__ is SubType) + self.assertTrue(hasattr(m, "a")) + + m.__class__ = types.ModuleType + self.assertTrue(m.__class__ is types.ModuleType) + self.assertFalse(hasattr(m, "a")) + def test_slots(self): # Testing __slots__... class C0(object): diff --git a/Misc/NEWS b/Misc/NEWS --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,6 +10,9 @@ Core and Builtins ----------------- +- Issue #22986: Allow changing an object's __class__ between a dynamic type and + static type in some cases. + - Issue #15859: PyUnicode_EncodeFSDefault(), PyUnicode_EncodeMBCS() and PyUnicode_EncodeCodePage() now raise an exception if the object is not an Unicode object. For PyUnicode_EncodeFSDefault(), it was already the case on diff --git a/Objects/typeobject.c b/Objects/typeobject.c --- a/Objects/typeobject.c +++ b/Objects/typeobject.c @@ -1196,8 +1196,11 @@ assert(basedealloc); basedealloc(self); - /* Can't reference self beyond this point */ - Py_DECREF(type); + /* Can't reference self beyond this point. It's possible tp_del switched + our type from a HEAPTYPE to a non-HEAPTYPE, so be careful about + reference counting. */ + if (type->tp_flags & Py_TPFLAGS_HEAPTYPE) + Py_DECREF(type); endlabel: ++_PyTrash_delete_nesting; @@ -3425,17 +3428,18 @@ } static int -equiv_structs(PyTypeObject *a, PyTypeObject *b) -{ - return a == b || - (a != NULL && - b != NULL && - a->tp_basicsize == b->tp_basicsize && - a->tp_itemsize == b->tp_itemsize && - a->tp_dictoffset == b->tp_dictoffset && - a->tp_weaklistoffset == b->tp_weaklistoffset && - ((a->tp_flags & Py_TPFLAGS_HAVE_GC) == - (b->tp_flags & Py_TPFLAGS_HAVE_GC))); +compatible_with_tp_base(PyTypeObject *child) +{ + PyTypeObject *parent = child->tp_base; + return (parent != NULL && + child->tp_basicsize == parent->tp_basicsize && + child->tp_itemsize == parent->tp_itemsize && + child->tp_dictoffset == parent->tp_dictoffset && + child->tp_weaklistoffset == parent->tp_weaklistoffset && + ((child->tp_flags & Py_TPFLAGS_HAVE_GC) == + (parent->tp_flags & Py_TPFLAGS_HAVE_GC)) && + (child->tp_dealloc == subtype_dealloc || + child->tp_dealloc == parent->tp_dealloc)); } static int @@ -3453,6 +3457,10 @@ size += sizeof(PyObject *); /* Check slots compliance */ + if (!(a->tp_flags & Py_TPFLAGS_HEAPTYPE) || + !(b->tp_flags & Py_TPFLAGS_HEAPTYPE)) { + return 0; + } slots_a = ((PyHeapTypeObject *)a)->ht_slots; slots_b = ((PyHeapTypeObject *)b)->ht_slots; if (slots_a && slots_b) { @@ -3468,9 +3476,7 @@ { PyTypeObject *newbase, *oldbase; - if (newto->tp_dealloc != oldto->tp_dealloc || - newto->tp_free != oldto->tp_free) - { + if (newto->tp_free != oldto->tp_free) { PyErr_Format(PyExc_TypeError, "%s assignment: " "'%s' deallocator differs from '%s'", @@ -3479,11 +3485,21 @@ oldto->tp_name); return 0; } + /* + It's tricky to tell if two arbitrary types are sufficiently compatible as + to be interchangeable; e.g., even if they have the same tp_basicsize, they + might have totally different struct fields. It's much easier to tell if a + type and its supertype are compatible; e.g., if they have the same + tp_basicsize, then that means they have identical fields. So to check + whether two arbitrary types are compatible, we first find the highest + supertype that each is compatible with, and then if those supertypes are + compatible then the original types must also be compatible. + */ newbase = newto; oldbase = oldto; - while (equiv_structs(newbase, newbase->tp_base)) + while (compatible_with_tp_base(newbase)) newbase = newbase->tp_base; - while (equiv_structs(oldbase, oldbase->tp_base)) + while (compatible_with_tp_base(oldbase)) oldbase = oldbase->tp_base; if (newbase != oldbase && (newbase->tp_base != oldbase->tp_base || @@ -3518,17 +3534,12 @@ return -1; } newto = (PyTypeObject *)value; - if (!(newto->tp_flags & Py_TPFLAGS_HEAPTYPE) || - !(oldto->tp_flags & Py_TPFLAGS_HEAPTYPE)) - { - PyErr_Format(PyExc_TypeError, - "__class__ assignment: only for heap types"); - return -1; - } if (compatible_for_assignment(oldto, newto, "__class__")) { - Py_INCREF(newto); + if (newto->tp_flags & Py_TPFLAGS_HEAPTYPE) + Py_INCREF(newto); Py_TYPE(self) = newto; - Py_DECREF(oldto); + if (oldto->tp_flags & Py_TPFLAGS_HEAPTYPE) + Py_DECREF(oldto); return 0; } else { -- Repository URL: https://hg.python.org/cpython