Issue #29019: Fix dict.fromkeys(x) overallocates when x is sparce dict.

Original patch by Rasmus Villemoes.

Misc/NEWS

@@ -13,6 +13,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #29019: Fix dict.fromkeys(x) overallocates when x is sparce dict.
+  Original patch by Rasmus Villemoes.
+
 - Issue #19542: Fix bugs in WeakValueDictionary.setdefault() and
   WeakValueDictionary.pop() when a GC collection happens in another
   thread.

Objects/dictobject.c

@@ -1391,7 +1391,7 @@ dict_fromkeys(PyObject *cls, PyObject *args)
             PyObject *key;
             long hash;
 
-            if (dictresize(mp, Py_SIZE(seq) / 2 * 3)) {
+            if (dictresize(mp, ((PyDictObject *)seq)->ma_used / 2 * 3)) {
                 Py_DECREF(d);
                 return NULL;
             }