From c26c1853eeb4c173d2a83e14d5f50d7edb58d30d Mon Sep 17 00:00:00 2001
From: Martin Teichmann <martin.teichmann@xfel.eu>
Date: Thu, 23 Feb 2017 15:23:33 +0100
Subject: [PATCH 1/3] bpo-30306: release arguments of contextmanager

The arguments of a function which was declared as a contextmanager
are stored inside the context manager, and thus are kept alive.

This is a possible unnecessary memory leak.
---
 Lib/contextlib.py           |  3 +++
 Lib/test/test_contextlib.py | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 962cedab490eb22..2f00dabf6ff38b7 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -83,6 +83,9 @@ def _recreate_cm(self):
         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 64b6578ff94eb30..ad0f0d92e0a2430 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -7,6 +7,7 @@
 import unittest
 from contextlib import *  # Tests __all__
 from test import support
+import weakref
 
 
 class TestAbstractContextManager(unittest.TestCase):
@@ -218,6 +219,21 @@ def woohoo(self, func, args, kwds):
         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
+
 
 class ClosingTestCase(unittest.TestCase):
 

From 0be196e6530bc9bcee68221d88e9421186352db7 Mon Sep 17 00:00:00 2001
From: Martin Teichmann <martin.teichmann@xfel.eu>
Date: Wed, 10 May 2017 08:31:59 +0200
Subject: [PATCH 2/3] add test for early creation of generator

---
 Lib/test/test_contextlib.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index ad0f0d92e0a2430..3deaa8be90a5ab4 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -234,6 +234,18 @@ def woohoo(a, b):
         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)
+
 
 class ClosingTestCase(unittest.TestCase):
 

From 33ed03e40b469326fb766978b53c04a0cfc76ffc Mon Sep 17 00:00:00 2001
From: Martin Teichmann <martin.teichmann@xfel.eu>
Date: Wed, 10 May 2017 09:58:15 +0200
Subject: [PATCH 3/3] add test for recursive context manager decorator

---
 Lib/test/test_contextlib.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 3deaa8be90a5ab4..76ff0d2204a9425 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -246,6 +246,25 @@ def woohoo(a, *, b):
         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):