Extend work on revision 52962: Eliminate redundant calls to PyObject_Hash().

Include/dictobject.h

@@ -100,12 +100,15 @@ PyAPI_FUNC(int) PyDict_DelItem(PyObject *mp, PyObject *key);
 PyAPI_FUNC(void) PyDict_Clear(PyObject *mp);
 PyAPI_FUNC(int) PyDict_Next(
 	PyObject *mp, Py_ssize_t *pos, PyObject **key, PyObject **value);
+PyAPI_FUNC(int) _PyDict_Next(
+	PyObject *mp, Py_ssize_t *pos, PyObject **key, PyObject **value, long *hash);
 PyAPI_FUNC(PyObject *) PyDict_Keys(PyObject *mp);
 PyAPI_FUNC(PyObject *) PyDict_Values(PyObject *mp);
 PyAPI_FUNC(PyObject *) PyDict_Items(PyObject *mp);
 PyAPI_FUNC(Py_ssize_t) PyDict_Size(PyObject *mp);
 PyAPI_FUNC(PyObject *) PyDict_Copy(PyObject *mp);
 PyAPI_FUNC(int) PyDict_Contains(PyObject *mp, PyObject *key);
+PyAPI_FUNC(int) _PyDict_Contains(PyObject *mp, PyObject *key, long hash);
 
 /* PyDict_Update(mp, other) is equivalent to PyDict_Merge(mp, other, 1). */
 PyAPI_FUNC(int) PyDict_Update(PyObject *mp, PyObject *other);

Lib/test/test_set.py

@@ -26,6 +26,14 @@ class ReprWrapper:
     def __repr__(self):
         return repr(self.value)
 
+class HashCountingInt(int):
+    'int-like object that counts the number of times __hash__ is called'
+    def __init__(self, *args):
+        self.hash_count = 0
+    def __hash__(self):
+        self.hash_count += 1
+        return int.__hash__(self)
+
 class TestJointOps(unittest.TestCase):
     # Tests common to both set and frozenset
 
@@ -270,6 +278,18 @@ class TestJointOps(unittest.TestCase):
             fo.close()
             os.remove(test_support.TESTFN)
 
+    def test_do_not_rehash_dict_keys(self):
+        n = 10
+        d = dict.fromkeys(map(HashCountingInt, xrange(n)))
+        self.assertEqual(sum(elem.hash_count for elem in d), n)
+        s = self.thetype(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)
+        s.difference(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)    
+        if hasattr(s, 'symmetric_difference_update'):
+            s.symmetric_difference_update(d)
+        self.assertEqual(sum(elem.hash_count for elem in d), n)      
+
 class TestSet(TestJointOps):
     thetype = set
 

Objects/dictobject.c

@@ -803,6 +803,34 @@ PyDict_Next(PyObject *op, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue)
 	return 1;
 }
 
+/* Internal version of PyDict_Next that returns a hash value in addition to the key and value.*/
+int
+_PyDict_Next(PyObject *op, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue, long *phash)
+{
+	register Py_ssize_t i;
+	register Py_ssize_t mask;
+	register dictentry *ep;
+
+	if (!PyDict_Check(op))
+		return 0;
+	i = *ppos;
+	if (i < 0)
+		return 0;
+	ep = ((dictobject *)op)->ma_table;
+	mask = ((dictobject *)op)->ma_mask;
+	while (i <= mask && ep[i].me_value == NULL)
+		i++;
+	*ppos = i+1;
+	if (i > mask)
+		return 0;
+        *phash = (long)(ep[i].me_hash);
+	if (pkey)
+		*pkey = ep[i].me_key;
+	if (pvalue)
+		*pvalue = ep[i].me_value;
+	return 1;
+}
+
 /* Methods */
 
 static void
@@ -1987,6 +2015,17 @@ PyDict_Contains(PyObject *op, PyObject *key)
 	return ep == NULL ? -1 : (ep->me_value != NULL);
 }
 
+/* Internal version of PyDict_Contains used when the hash value is already known */
+int
+_PyDict_Contains(PyObject *op, PyObject *key, long hash)
+{
+	dictobject *mp = (dictobject *)op;
+	dictentry *ep;
+
+	ep = (mp->ma_lookup)(mp, key, hash);
+	return ep == NULL ? -1 : (ep->me_value != NULL);
+}
+
 /* Hack to implement "key in dict" */
 static PySequenceMethods dict_as_sequence = {
 	0,			/* sq_length */

Objects/setobject.c

@@ -918,8 +918,14 @@ set_update_internal(PySetObject *so, PyObject *other)
 	if (PyDict_CheckExact(other)) {
 		PyObject *value;
 		Py_ssize_t pos = 0;
-		while (PyDict_Next(other, &pos, &key, &value)) {
-			if (set_add_key(so, key) == -1)
+		long hash;
+
+		while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
+			setentry an_entry;
+
+			an_entry.hash = hash;
+			an_entry.key = key;
+			if (set_add_entry(so, &an_entry) == -1)
 				return -1;
 		}
 		return 0;
@@ -1382,7 +1388,7 @@ set_difference(PySetObject *so, PyObject *other)
 			setentry entrycopy;
 			entrycopy.hash = entry->hash;
 			entrycopy.key = entry->key;
-			if (!PyDict_Contains(other, entry->key)) {
+			if (!_PyDict_Contains(other, entry->key, entry->hash)) {
 				if (set_add_entry((PySetObject *)result, &entrycopy) == -1) {
 					Py_DECREF(result);
 					return NULL;
@@ -1453,12 +1459,10 @@ set_symmetric_difference_update(PySetObject *so, PyObject *other)
 	if (PyDict_CheckExact(other)) {
 		PyObject *value;
 		int rv;
-		while (PyDict_Next(other, &pos, &key, &value)) {
+		long hash;
+		while (_PyDict_Next(other, &pos, &key, &value, &hash)) {
 			setentry an_entry;
-			long hash = PyObject_Hash(key);
 
-			if (hash == -1)
-				return NULL;
 			an_entry.hash = hash;
 			an_entry.key = key;
 			rv = set_discard_entry(so, &an_entry);