bpo-30040: new empty dict uses key-sharing dict (GH-1080)
Sizeof new empty dict becomes 72 bytes from 240 bytes (amd64).
It is same size to empty dict created by dict.clear().
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index fc885c5..e39fea6 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -5346,16 +5346,16 @@
a, b = A(), B()
self.assertEqual(sys.getsizeof(vars(a)), sys.getsizeof(vars(b)))
- self.assertLess(sys.getsizeof(vars(a)), sys.getsizeof({}))
+ self.assertLess(sys.getsizeof(vars(a)), sys.getsizeof({"a":1}))
# Initial hash table can contain at most 5 elements.
# Set 6 attributes to cause internal resizing.
a.x, a.y, a.z, a.w, a.v, a.u = range(6)
self.assertNotEqual(sys.getsizeof(vars(a)), sys.getsizeof(vars(b)))
a2 = A()
self.assertEqual(sys.getsizeof(vars(a)), sys.getsizeof(vars(a2)))
- self.assertLess(sys.getsizeof(vars(a)), sys.getsizeof({}))
+ self.assertLess(sys.getsizeof(vars(a)), sys.getsizeof({"a":1}))
b.u, b.v, b.w, b.t, b.s, b.r = range(6)
- self.assertLess(sys.getsizeof(vars(b)), sys.getsizeof({}))
+ self.assertLess(sys.getsizeof(vars(b)), sys.getsizeof({"a":1}))
class DebugHelperMeta(type):
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 92aefd8..4bd54af 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -982,8 +982,10 @@
check(int.__add__, size('3P2P'))
# method-wrapper (descriptor object)
check({}.__iter__, size('2P'))
+ # empty dict
+ check({}, size('nQ2P'))
# dict
- check({}, size('nQ2P') + calcsize('2nP2n') + 8 + (8*2//3)*calcsize('n2P'))
+ check({"a": 1}, size('nQ2P') + calcsize('2nP2n') + 8 + (8*2//3)*calcsize('n2P'))
longdict = {1:1, 2:2, 3:3, 4:4, 5:5, 6:6, 7:7, 8:8}
check(longdict, size('nQ2P') + calcsize('2nP2n') + 16 + (16*2//3)*calcsize('n2P'))
# dictionary-keyview
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-03-11-22-30-56.bpo-30040.W9z8X7.rst b/Misc/NEWS.d/next/Core and Builtins/2019-03-11-22-30-56.bpo-30040.W9z8X7.rst
new file mode 100644
index 0000000..eacba67
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-03-11-22-30-56.bpo-30040.W9z8X7.rst
@@ -0,0 +1,2 @@
+New empty dict uses fewer memory for now. It used more memory than empty
+dict created by ``dict.clear()``. Patch by Inada Naoki.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 83cadda..108c612 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -691,10 +691,8 @@
PyObject *
PyDict_New(void)
{
- PyDictKeysObject *keys = new_keys_object(PyDict_MINSIZE);
- if (keys == NULL)
- return NULL;
- return new_dict(keys, NULL);
+ dictkeys_incref(Py_EMPTY_KEYS);
+ return new_dict(Py_EMPTY_KEYS, empty_values);
}
/* Search index of hash table from offset of entry table */
@@ -1276,6 +1274,9 @@
Py_ssize_t newsize;
PyDictKeysObject *new_keys;
+ if (minused == 0) {
+ return PyDict_New();
+ }
/* There are no strict guarantee that returned dict can contain minused
* items without resize. So we create medium size dict instead of very
* large dict or MemoryError.