From 6edd2586082f62a5ac61af5acab77b63919faa47 Mon Sep 17 00:00:00 2001
From: "Phillip J. Eby" <pje@telecommunity.com>
Date: Sat, 25 Mar 2006 00:28:24 +0000
Subject: [PATCH] Fix a problem with @contextmanager not detecting a broken
 generator that yields after a throw().  Make @contextmanager not reraise
 exceptions, but return a false value in that case instead.  Add test cases
 for both behaviors.

---
 Lib/contextlib.py           |  5 ++++-
 Lib/test/test_contextlib.py | 22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 0a5d608503..282fc51004 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -30,9 +30,12 @@ class GeneratorContextManager(object):
         else:
             try:
                 self.gen.throw(type, value, traceback)
-                return True
+                raise RuntimeError("generator didn't stop after throw()")
             except StopIteration:
                 return True
+            except:
+                if sys.exc_info()[1] is not value:
+                    raise
 
 
 def contextmanager(func):
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index f8db88cc58..7d7f8d281c 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -45,6 +45,28 @@ class ContextManagerTestCase(unittest.TestCase):
             self.fail("Expected ZeroDivisionError")
         self.assertEqual(state, [1, 42, 999])
 
+    def test_contextmanager_no_reraise(self):
+        @contextmanager
+        def whee():
+            yield
+        ctx = whee().__context__()
+        ctx.__enter__()
+        # Calling __exit__ should not result in an exception
+        self.failIf(ctx.__exit__(TypeError, TypeError("foo"), None))
+
+    def test_contextmanager_trap_yield_after_throw(self):
+        @contextmanager
+        def whoo():
+            try:
+                yield
+            except:
+                yield
+        ctx = whoo().__context__()
+        ctx.__enter__()
+        self.assertRaises(
+            RuntimeError, ctx.__exit__, TypeError, TypeError("foo"), None
+        )
+
     def test_contextmanager_except(self):
         state = []
         @contextmanager
-- 
2.40.0