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bpo-40521: Empty frozenset is no longer a singleton (GH-21085)
* Revert "bpo-40521: Make the empty frozenset per interpreter (GH-21068)" This reverts commit 261cfed. * bpo-40521: Empty frozensets are no longer singletons * Complete the removal of the frozenset singleton
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Lines changed: 8 additions & 54 deletions

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‎Include/internal/pycore_interp.h‎

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@@ -244,8 +244,6 @@ struct _is {
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/* Using a cache is very effective since typically only a single slice is
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created and then deleted again. */
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PySliceObject *slice_cache;
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// The empty frozenset is a singleton.
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PyObject *empty_frozenset;
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struct _Py_tuple_state tuple;
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struct _Py_list_state list;

‎Include/internal/pycore_pylifecycle.h‎

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@@ -62,7 +62,6 @@ extern void _PyFrame_Fini(PyThreadState *tstate);
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extern void _PyDict_Fini(PyThreadState *tstate);
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extern void _PyTuple_Fini(PyThreadState *tstate);
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extern void _PyList_Fini(PyThreadState *tstate);
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extern void _PySet_Fini(PyThreadState *tstate);
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extern void _PyBytes_Fini(PyThreadState *tstate);
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extern void _PyFloat_Fini(PyThreadState *tstate);
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extern void _PySlice_Fini(PyThreadState *tstate);

‎Lib/test/test_marshal.py‎

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@@ -158,13 +158,6 @@ def test_sets(self):
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for constructor in (set, frozenset):
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self.helper(constructor(self.d.keys()))
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@support.cpython_only
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def test_empty_frozenset_singleton(self):
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# marshal.loads() must reuse the empty frozenset singleton
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obj = frozenset()
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obj2 = marshal.loads(marshal.dumps(obj))
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self.assertIs(obj2, obj)
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class BufferTestCase(unittest.TestCase, HelperMixin):
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‎Lib/test/test_set.py‎

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@@ -661,15 +661,6 @@ def test_init(self):
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s.__init__(self.otherword)
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self.assertEqual(s, set(self.word))
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def test_singleton_empty_frozenset(self):
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f = frozenset()
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efs = [frozenset(), frozenset([]), frozenset(()), frozenset(''),
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frozenset(), frozenset([]), frozenset(()), frozenset(''),
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frozenset(range(0)), frozenset(frozenset()),
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frozenset(f), f]
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# All of the empty frozensets should have just one id()
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self.assertEqual(len(set(map(id, efs))), 1)
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def test_constructor_identity(self):
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s = self.thetype(range(3))
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t = self.thetype(s)

‎Misc/NEWS.d/next/Core and Builtins/2020-05-20-01-17-34.bpo-40521.wvAehI.rst‎

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@@ -2,8 +2,9 @@ Each interpreter now its has own free lists, singletons and caches:
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* Free lists: float, tuple, list, dict, frame, context,
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asynchronous generator.
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* Singletons: empty tuple, empty frozenset, empty bytes string,
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* Singletons: empty tuple, empty bytes string,
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single byte character.
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* Slice cache.
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They are no longer shared by all interpreters.
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‎Misc/NEWS.d/next/Core and Builtins/2020-06-23-07-35-11.bpo-40521.dMNA6k.rst‎

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@@ -0,0 +1 @@
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Empty frozensets are no longer singletons.

‎Objects/setobject.c‎

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@@ -978,38 +978,16 @@ make_new_set_basetype(PyTypeObject *type, PyObject *iterable)
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static PyObject *
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make_new_frozenset(PyTypeObject *type, PyObject *iterable)
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{
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PyObject *res;
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if (type != &PyFrozenSet_Type) {
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return make_new_set(type, iterable);
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}
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if (iterable != NULL) {
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if (PyFrozenSet_CheckExact(iterable)) {
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/* frozenset(f) is idempotent */
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Py_INCREF(iterable);
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return iterable;
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}
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res = make_new_set((PyTypeObject *)type, iterable);
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if (res == NULL || PySet_GET_SIZE(res) != 0) {
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return res;
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}
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/* If the created frozenset is empty, return the empty frozenset singleton instead */
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Py_DECREF(res);
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if (iterable != NULL && PyFrozenSet_CheckExact(iterable)) {
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/* frozenset(f) is idempotent */
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Py_INCREF(iterable);
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return iterable;
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}
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// The empty frozenset is a singleton
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PyInterpreterState *interp = _PyInterpreterState_GET();
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res = interp->empty_frozenset;
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if (res == NULL) {
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interp->empty_frozenset = make_new_set((PyTypeObject *)type, NULL);
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res = interp->empty_frozenset;
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if (res == NULL) {
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return NULL;
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}
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}
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Py_INCREF(res);
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return res;
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return make_new_set((PyTypeObject *)type, iterable);
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}
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static PyObject *
@@ -2304,12 +2282,6 @@ PySet_Add(PyObject *anyset, PyObject *key)
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return set_add_key((PySetObject *)anyset, key);
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}
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void
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_PySet_Fini(PyThreadState *tstate)
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{
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Py_CLEAR(tstate->interp->empty_frozenset);
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}
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int
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_PySet_NextEntry(PyObject *set, Py_ssize_t *pos, PyObject **key, Py_hash_t *hash)
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{

‎Python/pylifecycle.c‎

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@@ -1253,7 +1253,6 @@ finalize_interp_types(PyThreadState *tstate, int is_main_interp)
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_PyAsyncGen_Fini(tstate);
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_PyContext_Fini(tstate);
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_PySet_Fini(tstate);
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_PyDict_Fini(tstate);
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_PyList_Fini(tstate);
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_PyTuple_Fini(tstate);

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