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[3.5] bpo-29692: contextlib.contextmanager may incorrectly unchain Ru… #1107

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Merged
merged 1 commit into from
Apr 13, 2017
Merged

[3.5] bpo-29692: contextlib.contextmanager may incorrectly unchain Ru… #1107

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12 changes: 6 additions & 6 deletions Lib/contextlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@ def __exit__(self, type, value, traceback):
try:
next(self.gen)
except StopIteration:
return
return False
else:
raise RuntimeError("generator didn't stop")
else:
Expand All @@ -87,7 +87,7 @@ def __exit__(self, type, value, traceback):
# Likewise, avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# (see PEP 479).
if exc.__cause__ is value:
if type is StopIteration and exc.__cause__ is value:
return False
raise
except:
Expand All @@ -98,10 +98,10 @@ def __exit__(self, type, value, traceback):
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
#
if sys.exc_info()[1] is not value:
raise
else:
raise RuntimeError("generator didn't stop after throw()")
if sys.exc_info()[1] is value:
return False
raise
raise RuntimeError("generator didn't stop after throw()")


def contextmanager(func):
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23 changes: 23 additions & 0 deletions Lib/test/test_contextlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,29 @@ def woohoo():
else:
self.fail('StopIteration was suppressed')

def test_contextmanager_do_not_unchain_non_stopiteration_exceptions(self):
@contextmanager
def test_issue29692():
try:
yield
except Exception as exc:
raise RuntimeError('issue29692:Chained') from exc
try:
with test_issue29692():
raise ZeroDivisionError
except Exception as ex:
self.assertIs(type(ex), RuntimeError)
self.assertEqual(ex.args[0], 'issue29692:Chained')
self.assertIsInstance(ex.__cause__, ZeroDivisionError)

try:
with test_issue29692():
raise StopIteration('issue29692:Unchained')
except Exception as ex:
self.assertIs(type(ex), StopIteration)
self.assertEqual(ex.args[0], 'issue29692:Unchained')
self.assertIsNone(ex.__cause__)

def _create_contextmanager_attribs(self):
def attribs(**kw):
def decorate(func):
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3 changes: 3 additions & 0 deletions Misc/NEWS
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,9 @@ Extension Modules

Library
-------
- bpo-29692: Fixed arbitrary unchaining of RuntimeError exceptions in
contextlib.contextmanager.
Patch by Siddharth Velankar.

- bpo-29998: Pickling and copying ImportError now preserves name and path
attributes.
Expand Down