bpo-30306: release arguments of contextmanager (GH-1500)
The arguments to a generator function which is declared as a
contextmanager are stored inside the context manager, and
thus are kept alive, even when it is used as a regular context
manager, and not as a function decorator (where it needs
the original arguments to recreate the generator on each
call).
This is a possible unnecessary memory leak, so this changes
contextmanager.__enter__ to release the saved arguments,
as that method being called means that particular CM instance
isn't going to need to recreate the underlying generator.
Patch by Martin Teichmann.
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index ef8f8c9..1ff8cdf 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -105,6 +105,9 @@
return self.__class__(self.func, self.args, self.kwds)
def __enter__(self):
+ # do not keep args and kwds alive unnecessarily
+ # they are only needed for recreation, which is not possible anymore
+ del self.args, self.kwds, self.func
try:
return next(self.gen)
except StopIteration:
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 96ceaa7..2a44404 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -8,6 +8,7 @@
import unittest
from contextlib import * # Tests __all__
from test import support
+import weakref
class TestAbstractContextManager(unittest.TestCase):
@@ -219,6 +220,52 @@
with woohoo(self=11, func=22, args=33, kwds=44) as target:
self.assertEqual(target, (11, 22, 33, 44))
+ def test_nokeepref(self):
+ class A:
+ pass
+
+ @contextmanager
+ def woohoo(a, b):
+ a = weakref.ref(a)
+ b = weakref.ref(b)
+ self.assertIsNone(a())
+ self.assertIsNone(b())
+ yield
+
+ with woohoo(A(), b=A()):
+ pass
+
+ def test_param_errors(self):
+ @contextmanager
+ def woohoo(a, *, b):
+ yield
+
+ with self.assertRaises(TypeError):
+ woohoo()
+ with self.assertRaises(TypeError):
+ woohoo(3, 5)
+ with self.assertRaises(TypeError):
+ woohoo(b=3)
+
+ def test_recursive(self):
+ depth = 0
+ @contextmanager
+ def woohoo():
+ nonlocal depth
+ before = depth
+ depth += 1
+ yield
+ depth -= 1
+ self.assertEqual(depth, before)
+
+ @woohoo()
+ def recursive():
+ if depth < 10:
+ recursive()
+
+ recursive()
+ self.assertEqual(depth, 0)
+
class ClosingTestCase(unittest.TestCase):