python · markshannon · Jul 1, 2022 · Jun 27, 2022 · Jun 27, 2022 · Jun 28, 2022
diff --git a/Include/internal/pycore_frame.h b/Include/internal/pycore_frame.h
@@ -210,6 +210,16 @@ PyGenObject *_PyFrame_GetGenerator(_PyInterpreterFrame *frame)
     return (PyGenObject *)(((char *)frame) - offset_in_gen);
 }
 
+/* Determine whether a frame is incomplete.
+ * A frame is incomplete until the first RESUME instruction
+ * as it may be part way through creating cell objects or a
+ * generator or coroutine. */
+static inline bool
+_PyFrame_IsIncomplete(_PyInterpreterFrame *frame)
+{
+    return frame->prev_instr < _PyCode_CODE(frame->f_code) + frame->f_code->_co_firsttraceable;
+}
+
 #ifdef __cplusplus
 }
 #endif

diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
@@ -170,6 +170,26 @@ def f():
             g.send(0)
         self.assertEqual(next(g), 1)
 
+    def test_handle_frame_object_in_creation(self):
+
+        def cb(*args):
+            try:
+                sys._getframe(1)
+            except ValueError:
+                pass
+
+        def gen():
+            yield 1
+
+        thresholds = gc.get_threshold()
+        gc.callbacks.append(cb)
+        gc.set_threshold(1, 0, 0)
+
+        try:
+            gen()
+        finally:
+            gc.set_threshold(*thresholds)
+            gc.callbacks.pop()
 
 class ExceptionTest(unittest.TestCase):
     # Tests for the issue #23353: check that the currently handled exception

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-06-28-10-08-06.gh-issue-94262.m-HWUZ.rst b/Misc/NEWS.d/next/Core and Builtins/2022-06-28-10-08-06.gh-issue-94262.m-HWUZ.rst
@@ -0,0 +1,3 @@
+Don't create frame objects for incomplete frames. Prevents the creation of
+generators and closures from being observable to Python and C extensions,
+restoring the behavior of 3.10 and earlier.
diff --git a/Python/frame.c b/Python/frame.c
@@ -68,9 +68,13 @@ take_ownership(PyFrameObject *f, _PyInterpreterFrame *frame)
     f->f_frame = frame;
     frame->owner = FRAME_OWNED_BY_FRAME_OBJECT;
     assert(f->f_back == NULL);
-    if (frame->previous != NULL) {
+    _PyInterpreterFrame *prev = frame->previous;
+    while (prev && _PyFrame_IsIncomplete(prev)) {
+        prev = prev->previous;
+    }
+    if (prev) {
         /* Link PyFrameObjects.f_back and remove link through _PyInterpreterFrame.previous */
-        PyFrameObject *back = _PyFrame_GetFrameObject(frame->previous);
+        PyFrameObject *back = _PyFrame_GetFrameObject(prev);
         if (back == NULL) {
             /* Memory error here. */
             assert(PyErr_ExceptionMatches(PyExc_MemoryError));

@@ -1776,9 +1776,17 @@ sys__getframe_impl(PyObject *module, int depth)
         return NULL;
     }
 
-    while (depth > 0 && frame != NULL) {
-        frame = frame->previous;
-        --depth;
+    if (frame != NULL) {
+        while (depth > 0) {
+            frame = frame->previous;
+            if (frame == NULL) {
+                break;
+            }
+            if (_PyFrame_IsIncomplete(frame)) {
+                continue;
+            }
+            --depth;
+        }
     }
     if (frame == NULL) {
         _PyErr_SetString(tstate, PyExc_ValueError,