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bpo-44206: Add a version number to dictionary keys (GH-26333)
* Store log2(size) instead of size in dict-keys. * Use enum instead of function pointer to record kind of keys. * Add version number to dict keys.
1 parent 8994e9c commit f8a95df

7 files changed

Lines changed: 223 additions & 317 deletions

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‎Include/cpython/dictobject.h‎

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

‎Lib/test/test_ordered_dict.py‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -752,7 +752,7 @@ def test_sizeof_exact(self):
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check = self.check_sizeof
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basicsize = size('nQ2P' + '3PnPn2P')
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keysize = calcsize('2nP2n')
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keysize = calcsize('n2BI2n')
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entrysize = calcsize('n2P')
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p = calcsize('P')

‎Lib/test/test_sys.py‎

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
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# strings to intern in test_intern()
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INTERN_NUMRUNS = 0
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DICT_KEY_STRUCT_FORMAT = 'n2BI2n'
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class DisplayHookTest(unittest.TestCase):
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@@ -1229,9 +1230,9 @@ def inner():
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# empty dict
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check({}, size('nQ2P'))
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# dict
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check({"a": 1}, size('nQ2P') + calcsize('2nP2n') + 8 + (8*2//3)*calcsize('n2P'))
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check({"a": 1}, size('nQ2P') + calcsize(DICT_KEY_STRUCT_FORMAT) + 8 + (8*2//3)*calcsize('n2P'))
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longdict = {1:1, 2:2, 3:3, 4:4, 5:5, 6:6, 7:7, 8:8}
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check(longdict, size('nQ2P') + calcsize('2nP2n') + 16 + (16*2//3)*calcsize('n2P'))
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check(longdict, size('nQ2P') + calcsize(DICT_KEY_STRUCT_FORMAT) + 16 + (16*2//3)*calcsize('n2P'))
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# dictionary-keyview
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check({}.keys(), size('P'))
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# dictionary-valueview
@@ -1385,13 +1386,13 @@ def delx(self): del self.__x
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'5P')
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class newstyleclass(object): pass
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# Separate block for PyDictKeysObject with 8 keys and 5 entries
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check(newstyleclass, s + calcsize("2nP2n0P") + 8 + 5*calcsize("n2P"))
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check(newstyleclass, s + calcsize(DICT_KEY_STRUCT_FORMAT) + 8 + 5*calcsize("n2P"))
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# dict with shared keys
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check(newstyleclass().__dict__, size('nQ2P') + 5*self.P)
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o = newstyleclass()
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o.a = o.b = o.c = o.d = o.e = o.f = o.g = o.h = 1
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# Separate block for PyDictKeysObject with 16 keys and 10 entries
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check(newstyleclass, s + calcsize("2nP2n0P") + 16 + 10*calcsize("n2P"))
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check(newstyleclass, s + calcsize(DICT_KEY_STRUCT_FORMAT) + 16 + 10*calcsize("n2P"))
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# dict with shared keys
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check(newstyleclass().__dict__, size('nQ2P') + 10*self.P)
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# unicode

‎Objects/dict-common.h‎

Lines changed: 14 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -8,37 +8,34 @@ typedef struct {
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PyObject *me_value; /* This field is only meaningful for combined tables */
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} PyDictKeyEntry;
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/* dict_lookup_func() returns index of entry which can be used like DK_ENTRIES(dk)[index].
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/* _Py_dict_lookup() returns index of entry which can be used like DK_ENTRIES(dk)[index].
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* -1 when no entry found, -3 when compare raises error.
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*/
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typedef Py_ssize_t (*dict_lookup_func)
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(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
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Py_ssize_t _Py_dict_lookup(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
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#define DKIX_EMPTY (-1)
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#define DKIX_DUMMY (-2) /* Used internally */
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#define DKIX_ERROR (-3)
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typedef enum {
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DICT_KEYS_GENERAL = 0,
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DICT_KEYS_UNICODE = 1,
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DICT_KEYS_SPLIT = 2
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} DictKeysKind;
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/* See dictobject.c for actual layout of DictKeysObject */
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struct _dictkeysobject {
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Py_ssize_t dk_refcnt;
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/* Size of the hash table (dk_indices). It must be a power of 2. */
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Py_ssize_t dk_size;
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/* Function to lookup in the hash table (dk_indices):
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- lookdict(): general-purpose, and may return DKIX_ERROR if (and
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only if) a comparison raises an exception.
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- lookdict_unicode(): specialized to Unicode string keys, comparison of
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which can never raise an exception; that function can never return
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DKIX_ERROR.
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uint8_t dk_log2_size;
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- lookdict_unicode_nodummy(): similar to lookdict_unicode() but further
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specialized for Unicode string keys that cannot be the <dummy> value.
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/* Kind of keys */
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uint8_t dk_kind;
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- lookdict_split(): Version of lookdict() for split tables. */
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dict_lookup_func dk_lookup;
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/* Version number -- Reset to 0 by any modification to keys */
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uint32_t dk_version;
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/* Number of usable entries in dk_entries. */
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Py_ssize_t dk_usable;

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