[issue38525] Strange reversed dict behavior

[Inada Naoki]

Inada Naoki <songofacandy at gmail.com> added the comment:

When dict is empty, di_pos of reverse iterator must be -1, not 0.
Additionally, di_pos must be initialized from ma_used when dict is key sharing dict.

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 64876e0519..6c4b41700b 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -3452,10 +3452,15 @@ dictiter_new(PyDictObject *dict, PyTypeObject *itertype)
     di->di_dict = dict;
     di->di_used = dict->ma_used;
     di->len = dict->ma_used;
-    if ((itertype == &PyDictRevIterKey_Type ||
-         itertype == &PyDictRevIterItem_Type ||
-         itertype == &PyDictRevIterValue_Type) && dict->ma_used) {
+    if (itertype == &PyDictRevIterKey_Type ||
+            itertype == &PyDictRevIterItem_Type ||
+            itertype == &PyDictRevIterValue_Type) {
+        if (dict->ma_values) {
+            di->di_pos = dict->ma_used - 1;
+        }
+        else {
             di->di_pos = dict->ma_keys->dk_nentries - 1;
+        }
     }
     else {

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38525>
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