python
diff --git a/‎Lib/test/test_iter.py‎
Lines changed: 25 additions & 0 deletions b/‎Lib/test/test_iter.py‎
Lines changed: 25 additions & 0 deletions
diff --git a/‎Misc/NEWS.d/next/Library/2023-02-14-09-08-48.gh-issue-101892.FMos8l.rst‎
Lines changed: 3 additions & 0 deletions b/‎Misc/NEWS.d/next/Library/2023-02-14-09-08-48.gh-issue-101892.FMos8l.rst‎
Lines changed: 3 additions & 0 deletions
diff --git a/‎Objects/iterobject.c‎
Lines changed: 2 additions & 2 deletions b/‎Objects/iterobject.c‎
Lines changed: 2 additions & 2 deletions
@@ -346,6 +346,31 @@ def spam(state=[0]):
             return i
         self.check_iterator(iter(spam, 20), list(range(10)), pickle=False)
 
+    def test_iter_function_concealing_reentrant_exhaustion(self):
+        # gh-101892: Test two-argument iter() with a function that
+        # exhausts its associated iterator but forgets to either return
+        # a sentinel value or raise StopIteration.
+        HAS_MORE = 1
+        NO_MORE = 2
+
+        def exhaust(iterator):
+            """Exhaust an iterator without raising StopIteration."""
+            list(iterator)
+
+        def spam():
+            # Touching the iterator with exhaust() below will call
+            # spam() once again so protect against recursion.
+            if spam.is_recursive_call:
+                return NO_MORE
+            spam.is_recursive_call = True
+            exhaust(spam.iterator)
+            return HAS_MORE
+
+        spam.is_recursive_call = False
+        spam.iterator = iter(spam, NO_MORE)
+        with self.assertRaises(StopIteration):
+            next(spam.iterator)
+
     # Test exception propagation through function iterator
     def test_exception_function(self):
         def spam(state=[0]):
 
@@ -0,0 +1,3 @@
+Callable iterators no longer raise :class:`SystemError` when the
+callable object exhausts the iterator but forgets to either return a
+sentinel value or raise :class:`StopIteration`.
@@ -223,15 +223,14 @@ calliter_iternext(calliterobject *it)
     }
 
     result = _PyObject_CallNoArg(it->it_callable);
-    if (result != NULL) {
+    if (result != NULL && it->it_sentinel != NULL){
         int ok;
 
         ok = PyObject_RichCompareBool(it->it_sentinel, result, Py_EQ);
         if (ok == 0) {
             return result; /* Common case, fast path */
         }
 
-        Py_DECREF(result);
         if (ok > 0) {
             Py_CLEAR(it->it_callable);
             Py_CLEAR(it->it_sentinel);
@@ -242,6 +241,7 @@ calliter_iternext(calliterobject *it)
         Py_CLEAR(it->it_callable);
         Py_CLEAR(it->it_sentinel);
     }
+    Py_XDECREF(result);
     return NULL;
 }
Original file line number	Diff line number	Diff line change
@@ -0,0 +1,3 @@
	1	+ Callable iterators no longer raise :class:`SystemError` when the
	2	+ callable object exhausts the iterator but forgets to either return a
	3	+ sentinel value or raise :class:`StopIteration`.
Original file line number	Diff line number	Diff line change
@@ -223,15 +223,14 @@ calliter_iternext(calliterobject *it)
223	223	}
224	224
225	225	result = _PyObject_CallNoArg(it->it_callable);
226		- if (result != NULL) {
	226	+ if (result != NULL && it->it_sentinel != NULL){
227	227	int ok;
228	228
229	229	ok = PyObject_RichCompareBool(it->it_sentinel, result, Py_EQ);
230	230	if (ok == 0) {
231	231	return result; /* Common case, fast path */
232	232	}
233	233
234		- Py_DECREF(result);
235	234	if (ok > 0) {
236	235	Py_CLEAR(it->it_callable);
237	236	Py_CLEAR(it->it_sentinel);
@@ -242,6 +241,7 @@ calliter_iternext(calliterobject *it)
242	241	Py_CLEAR(it->it_callable);
243	242	Py_CLEAR(it->it_sentinel);
244	243	}
	244	+ Py_XDECREF(result);
245	245	return NULL;
246	246	}
247	247