iffisNone:f=sys._getframe().f_back.f_back

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.pyindex 149d0234fe..48d5c1a809 100644--- a/Lib/test/test_traceback.py+++ b/Lib/test/test_traceback.py@@ -2241,8 +2241,7 @@ class TestStack(unittest.TestCase):     def test_walk_stack(self):         def deeper():             return list(traceback.walk_stack(None))-        s1 = list(traceback.walk_stack(None))-        s2 = deeper()+        s1, s2 = list(traceback.walk_stack(None)), deeper()         self.assertEqual(len(s2) - len(s1), 1)         self.assertEqual(s2[1:], s1)diff --git a/Lib/traceback.py b/Lib/traceback.pyindex cf5f355ff0..701ce9e4bb 100644--- a/Lib/traceback.py+++ b/Lib/traceback.py@@ -323,17 +323,21 @@ def line(self):         return self._line.strip()-def walk_stack(f):+def walk_stack(frame):     """Walk a stack yielding the frame and line number for each frame.     This will follow f.f_back from the given frame. If no frame is given, the     current stack is used. Usually used with StackSummary.extract.     """-    if f is None:-        f = sys._getframe().f_back.f_back.f_back.f_back-    while f is not None:-        yield f, f.f_lineno-        f = f.f_back+    if frame is None:+        frame = sys._getframe().f_back++    def walk_stack_generator(f):+        while f is not None:+            yield f, f.f_lineno+            f = f.f_back++    return walk_stack_generator(frame)