bpo-44206: Add a version number to dictionary keys

Include/cpython/dictobject.h

@@ -82,3 +82,7 @@ typedef struct {
 
 PyAPI_FUNC(PyObject *) _PyDictView_New(PyObject *, PyTypeObject *);
 PyAPI_FUNC(PyObject *) _PyDictView_Intersect(PyObject* self, PyObject *other);
+
+/* Gets a version number unique to the current state of the keys of dict, if possible.
+ * Returns the version number, or zero if it was not possible to get a version number. */
+uint32_t _PyDictKeys_GetVersionForCurrentState(PyDictObject *dict);

Lib/test/test_ordered_dict.py

@@ -752,7 +752,7 @@ def test_sizeof_exact(self):
         check = self.check_sizeof
 
         basicsize = size('nQ2P' + '3PnPn2P')
-        keysize = calcsize('2nP2n')
+        keysize = calcsize('n2BI2n')
 
         entrysize = calcsize('n2P')
         p = calcsize('P')

Lib/test/test_sys.py

@@ -22,6 +22,7 @@
 # strings to intern in test_intern()
 INTERN_NUMRUNS = 0
 
+DICT_KEY_STRUCT_FORMAT = 'n2BI2n'
 
 class DisplayHookTest(unittest.TestCase):
 
@@ -1229,9 +1230,9 @@ def inner():
         # empty dict
         check({}, size('nQ2P'))
         # dict
-        check({"a": 1}, size('nQ2P') + calcsize('2nP2n') + 8 + (8*2//3)*calcsize('n2P'))
+        check({"a": 1}, size('nQ2P') + calcsize(DICT_KEY_STRUCT_FORMAT) + 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'))
+        check(longdict, size('nQ2P') + calcsize(DICT_KEY_STRUCT_FORMAT) + 16 + (16*2//3)*calcsize('n2P'))
         # dictionary-keyview
         check({}.keys(), size('P'))
         # dictionary-valueview
@@ -1385,13 +1386,13 @@ def delx(self): del self.__x
                   '5P')
         class newstyleclass(object): pass
         # Separate block for PyDictKeysObject with 8 keys and 5 entries
-        check(newstyleclass, s + calcsize("2nP2n0P") + 8 + 5*calcsize("n2P"))
+        check(newstyleclass, s + calcsize(DICT_KEY_STRUCT_FORMAT) + 8 + 5*calcsize("n2P"))
         # dict with shared keys
         check(newstyleclass().__dict__, size('nQ2P') + 5*self.P)
         o = newstyleclass()
         o.a = o.b = o.c = o.d = o.e = o.f = o.g = o.h = 1
         # Separate block for PyDictKeysObject with 16 keys and 10 entries
-        check(newstyleclass, s + calcsize("2nP2n0P") + 16 + 10*calcsize("n2P"))
+        check(newstyleclass, s + calcsize(DICT_KEY_STRUCT_FORMAT) + 16 + 10*calcsize("n2P"))
         # dict with shared keys
         check(newstyleclass().__dict__, size('nQ2P') + 10*self.P)
         # unicode

Objects/dict-common.h

@@ -8,37 +8,34 @@ typedef struct {
     PyObject *me_value; /* This field is only meaningful for combined tables */
 } PyDictKeyEntry;
 
-/* dict_lookup_func() returns index of entry which can be used like DK_ENTRIES(dk)[index].
+/* _Py_dict_lookup() returns index of entry which can be used like DK_ENTRIES(dk)[index].
  * -1 when no entry found, -3 when compare raises error.
  */
-typedef Py_ssize_t (*dict_lookup_func)
-    (PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
+Py_ssize_t _Py_dict_lookup(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
+
 
 #define DKIX_EMPTY (-1)
 #define DKIX_DUMMY (-2)  /* Used internally */
 #define DKIX_ERROR (-3)
 
+typedef enum {
+    DICT_KEYS_GENERAL = 0,
+    DICT_KEYS_UNICODE = 1,
+    DICT_KEYS_SPLIT = 2
+} DictKeysKind;
+
 /* See dictobject.c for actual layout of DictKeysObject */
 struct _dictkeysobject {
     Py_ssize_t dk_refcnt;
 
     /* Size of the hash table (dk_indices). It must be a power of 2. */
-    Py_ssize_t dk_size;
-
-    /* Function to lookup in the hash table (dk_indices):
-
-       - lookdict(): general-purpose, and may return DKIX_ERROR if (and
-         only if) a comparison raises an exception.
-
-       - lookdict_unicode(): specialized to Unicode string keys, comparison of
-         which can never raise an exception; that function can never return
-         DKIX_ERROR.
+    uint8_t dk_log2_size;
 
-       - lookdict_unicode_nodummy(): similar to lookdict_unicode() but further
-         specialized for Unicode string keys that cannot be the <dummy> value.
+    /* Kind of keys */
+    uint8_t dk_kind;
 
-       - lookdict_split(): Version of lookdict() for split tables. */
-    dict_lookup_func dk_lookup;
+    /* Version number -- Reset to 0 by any modification to keys */
+    uint32_t dk_version;
 
     /* Number of usable entries in dk_entries. */
     Py_ssize_t dk_usable;