From 5d44c08f1c18583d568283170454bab0c11f8257 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Mon, 2 Feb 2015 18:36:31 +0100
Subject: Issue #23353, asyncio: Workaround CPython bug #23353

Don't use yield/yield-from in an except block of a generator. Store the
exception and handle it outside the except block.
---
 Lib/asyncio/test_utils.py     |  4 ++++
 Lib/asyncio/unix_events.py    | 12 ++++++++++--
 Lib/asyncio/windows_events.py | 11 +++++++++--
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/Lib/asyncio/test_utils.py b/Lib/asyncio/test_utils.py
index 6eedc58..8cee95b 100644
--- a/Lib/asyncio/test_utils.py
+++ b/Lib/asyncio/test_utils.py
@@ -416,6 +416,10 @@ class TestCase(unittest.TestCase):
     def tearDown(self):
         events.set_event_loop(None)
 
+        # Detect CPython bug #23353: ensure that yield/yield-from is not used
+        # in an except block of a generator
+        self.assertEqual(sys.exc_info(), (None, None, None))
+
 
 @contextlib.contextmanager
 def disable_logger():
diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index 1fc39ab..75e7c9c 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -186,10 +186,18 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                                       self._child_watcher_callback, transp)
             try:
                 yield from waiter
-            except:
+            except Exception as exc:
+                # Workaround CPython bug #23353: using yield/yield-from in an
+                # except block of a generator doesn't clear properly
+                # sys.exc_info()
+                err = exc
+            else:
+                err = None
+
+            if err is not None:
                 transp.close()
                 yield from transp._wait()
-                raise
+                raise err
 
         return transp
 
diff --git a/Lib/asyncio/windows_events.py b/Lib/asyncio/windows_events.py
index c4bffc4..f311e46 100644
--- a/Lib/asyncio/windows_events.py
+++ b/Lib/asyncio/windows_events.py
@@ -373,10 +373,17 @@ class ProactorEventLoop(proactor_events.BaseProactorEventLoop):
                                              **kwargs)
         try:
             yield from waiter
-        except:
+        except Exception as exc:
+            # Workaround CPython bug #23353: using yield/yield-from in an
+            # except block of a generator doesn't clear properly sys.exc_info()
+            err = exc
+        else:
+            err = None
+
+        if err is not None:
             transp.close()
             yield from transp._wait()
-            raise
+            raise err
 
         return transp
 
-- 
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