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bpo-40521: Empty frozenset is no longer a singleton #21085

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Merged
vstinner merged 3 commits into from
Jun 23, 2020
Merged

bpo-40521: Empty frozenset is no longer a singleton #21085

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00c029a
Revert "bpo-40521: Make the empty frozenset per interpreter (GH-21068)"
rhettinger Jun 23, 2020
da8e997
bpo-40521: Empty frozensets are no longer singletons
rhettinger Jun 23, 2020
a29440c
Complete the removal of the frozenset singleton
rhettinger Jun 23, 2020
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bpo-40521: Empty frozensets are no longer singletons
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@rhettinger
rhettinger committed Jun 23, 2020
commit da8e997a082ffea1c0109d2b0d850ae23da77d32
7 changes: 0 additions & 7 deletions Lib/test/test_marshal.py
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Expand Up @@ -158,13 +158,6 @@ def test_sets(self):
for constructor in (set, frozenset):
self.helper(constructor(self.d.keys()))

@support.cpython_only
def test_empty_frozenset_singleton(self):
# marshal.loads() must reuse the empty frozenset singleton
obj = frozenset()
obj2 = marshal.loads(marshal.dumps(obj))
self.assertIs(obj2, obj)


class BufferTestCase(unittest.TestCase, HelperMixin):

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9 changes: 0 additions & 9 deletions Lib/test/test_set.py
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Expand Up @@ -661,15 +661,6 @@ def test_init(self):
s.__init__(self.otherword)
self.assertEqual(s, set(self.word))

def test_singleton_empty_frozenset(self):
f = frozenset()
efs = [frozenset(), frozenset([]), frozenset(()), frozenset(''),
frozenset(), frozenset([]), frozenset(()), frozenset(''),
frozenset(range(0)), frozenset(frozenset()),
frozenset(f), f]
# All of the empty frozensets should have just one id()
self.assertEqual(len(set(map(id, efs))), 1)

def test_constructor_identity(self):
s = self.thetype(range(3))
t = self.thetype(s)
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-06-23-07-35-11.bpo-40521.dMNA6k.rst
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@@ -0,0 +1 @@
Empty frozensets are no longer singletons.
27 changes: 5 additions & 22 deletions Objects/setobject.c
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Expand Up @@ -975,36 +975,19 @@ make_new_set_basetype(PyTypeObject *type, PyObject *iterable)
return make_new_set(type, iterable);
}

/* The empty frozenset is a singleton */
static PyObject *emptyfrozenset = NULL;

static PyObject *
make_new_frozenset(PyTypeObject *type, PyObject *iterable)
{
if (type != &PyFrozenSet_Type) {
return make_new_set(type, iterable);
}

if (iterable != NULL) {
if (PyFrozenSet_CheckExact(iterable)) {
/* frozenset(f) is idempotent */
Py_INCREF(iterable);
return iterable;
}
PyObject *res = make_new_set((PyTypeObject *)type, iterable);
if (res == NULL || PySet_GET_SIZE(res) != 0) {
return res;
if (iterable != NULL && PyFrozenSet_CheckExact(iterable)) {
/* frozenset(f) is idempotent */
Py_INCREF(iterable);
return iterable;
}
/* If the created frozenset is empty, return the empty frozenset singleton instead */
Py_DECREF(res);
}

// The empty frozenset is a singleton
if (emptyfrozenset == NULL) {
emptyfrozenset = make_new_set((PyTypeObject *)type, NULL);
}
Py_XINCREF(emptyfrozenset);
return emptyfrozenset;
return make_new_set((PyTypeObject *)type, iterable);
}

static PyObject *
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