From 83195c3f0cffc571e265ca7e42cbbe1f27c792e1 Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Sun, 3 Jul 2011 13:44:00 -0500
Subject: [PATCH] restore a generator's caller's exception state both on yield
 and (last) return

This prevents generator exception state from leaking into the caller.

Closes #12475.
---
 Lib/test/test_exceptions.py | 15 +++++++++++++++
 Misc/NEWS                   |  3 +++
 Python/ceval.c              |  9 +++++----
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 76f4249490f..ad9a19e6fd4 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -566,6 +566,21 @@ class ExceptionTests(unittest.TestCase):
             del g
             self.assertEqual(sys.exc_info()[0], TypeError)
 
+    def test_generator_leaking2(self):
+        # See issue 12475.
+        def g():
+            yield
+        try:
+            raise RuntimeError
+        except RuntimeError:
+            it = g()
+            next(it)
+        try:
+            next(it)
+        except StopIteration:
+            pass
+        self.assertEqual(sys.exc_info(), (None, None, None))
+
     def test_generator_finalizing_and_exc_info(self):
         # See #7173
         def simple_gen():
diff --git a/Misc/NEWS b/Misc/NEWS
index e0aaa8d717c..a05cc36aa39 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.2.2?
 Core and Builtins
 -----------------
 
+- Issue #12475: Prevent generators from leaking their exception state into the
+  callers frame as they return for the last time.
+
 Library
 -------
 
diff --git a/Python/ceval.c b/Python/ceval.c
index 705ed415a9c..c0f2874a8f2 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1881,10 +1881,6 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
             retval = POP();
             f->f_stacktop = stack_pointer;
             why = WHY_YIELD;
-            /* Put aside the current exception state and restore
-               that of the calling frame. This only serves when
-               "yield" is used inside an except handler. */
-            SWAP_EXC_STATE();
             goto fast_yield;
 
         TARGET(POP_EXCEPT)
@@ -3021,6 +3017,11 @@ fast_block_end:
         retval = NULL;
 
 fast_yield:
+    if (co->co_flags & CO_GENERATOR && (why == WHY_YIELD || why == WHY_RETURN))
+        /* Put aside the current exception state and restore that of the
+           calling frame. */
+        SWAP_EXC_STATE();
+
     if (tstate->use_tracing) {
         if (tstate->c_tracefunc) {
             if (why == WHY_RETURN || why == WHY_YIELD) {