Fix issue #1705170 (backport from trunk)

3 files changed, 24 insertions, 0 deletions

diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index a807c42ce4..c4fab1bbfa 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -25,6 +25,10 @@ class GeneratorContextManager(object):
             else:
                 raise RuntimeError("generator didn't stop")
         else:
+            if value is None:
+                # Need to force instantiation so we can reliably
+                # tell if we get the same exception back
+                value = type()
             try:
                 self.gen.throw(type, value, traceback)
                 raise RuntimeError("generator didn't stop after throw()")
diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
index 57505085dd..8242c912c5 100644
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -440,6 +440,7 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
         self.assertAfterWithGeneratorInvariantsNoError(self.bar)
 
     def testRaisedStopIteration1(self):
+        # From bug 1462485
         @contextmanager
         def cm():
             yield
@@ -451,6 +452,7 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
         self.assertRaises(StopIteration, shouldThrow)
 
     def testRaisedStopIteration2(self):
+        # From bug 1462485
         class cm(object):
             def __enter__(self):
                 pass
@@ -463,7 +465,21 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
 
         self.assertRaises(StopIteration, shouldThrow)
 
+    def testRaisedStopIteration3(self):
+        # Another variant where the exception hasn't been instantiated
+        # From bug 1705170
+        @contextmanager
+        def cm():
+            yield
+
+        def shouldThrow():
+            with cm():
+                raise iter([]).next()
+
+        self.assertRaises(StopIteration, shouldThrow)
+
     def testRaisedGeneratorExit1(self):
+        # From bug 1462485
         @contextmanager
         def cm():
             yield
@@ -475,6 +491,7 @@ class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
         self.assertRaises(GeneratorExit, shouldThrow)
 
     def testRaisedGeneratorExit2(self):
+        # From bug 1462485
         class cm (object):
             def __enter__(self):
                 pass
diff --git a/Misc/NEWS b/Misc/NEWS
index 2cf7be4108..aad83fd1c1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -32,6 +32,9 @@ Core and builtins
 Library
 -------
 
+- Issue #1705170: contextlib.contextmanager was still swallowing
+  StopIteration in some cases. This should no longer happen.
+
 - Bug #1307: Fix smtpd so it doesn't raise an exception when there is no arg.
 
 - ctypes will now work correctly on 32-bit systems when Python is