From 4661a7022289b0ee35b045c899b53363b9e925d4 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 28 Apr 2017 19:17:26 +0300
Subject: [PATCH 1/2] [2.7] bpo-30197: Enhance swap_attr() and backport
 swap_item() in test.test_support. (#1341)

(cherry picked from commit d1a1def7bf221b04dcf3fc3a67aa19aa2f622f83)
---
 Lib/test/test_support.py  | 39 +++++++++++++++++++++++++++++++++++++--
 Lib/test/test_tempfile.py |  5 ++---
 Misc/NEWS                 |  6 ++++++
 3 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index e339da5ff4d1d3..976f301c0a9144 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -1647,12 +1647,15 @@ def swap_attr(obj, attr, new_val):
         restoring the old value at the end of the block. If `attr` doesn't
         exist on `obj`, it will be created and then deleted at the end of the
         block.
+
+        The old value (or None if it doesn't exist) will be assigned to the
+        target of the "as" clause, if there is one.
     """
     if hasattr(obj, attr):
         real_val = getattr(obj, attr)
         setattr(obj, attr, new_val)
         try:
-            yield
+            yield real_val
         finally:
             setattr(obj, attr, real_val)
     else:
@@ -1660,7 +1663,39 @@ def swap_attr(obj, attr, new_val):
         try:
             yield
         finally:
-            delattr(obj, attr)
+            if hasattr(obj, attr):
+                delattr(obj, attr)
+
+@contextlib.contextmanager
+def swap_item(obj, item, new_val):
+    """Temporary swap out an item with a new object.
+
+    Usage:
+        with swap_item(obj, "item", 5):
+            ...
+
+        This will set obj["item"] to 5 for the duration of the with: block,
+        restoring the old value at the end of the block. If `item` doesn't
+        exist on `obj`, it will be created and then deleted at the end of the
+        block.
+
+        The old value (or None if it doesn't exist) will be assigned to the
+        target of the "as" clause, if there is one.
+    """
+    if item in obj:
+        real_val = obj[item]
+        obj[item] = new_val
+        try:
+            yield real_val
+        finally:
+            obj[item] = real_val
+    else:
+        obj[item] = new_val
+        try:
+            yield
+        finally:
+            if item in obj:
+                del obj[item]
 
 def py3k_bytes(b):
     """Emulate the py3k bytes() constructor.
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 078e4a9a2d06a9..5c85cc9bd306d4 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -235,13 +235,12 @@ def raise_OSError(*args, **kwargs):
                     self.assertEqual(cm.exception.errno, errno.ENOENT)
                     self.assertEqual(os.listdir(our_temp_directory), [])
 
-                open = io.open
                 def bad_writer(*args, **kwargs):
-                    fp = open(*args, **kwargs)
+                    fp = orig_open(*args, **kwargs)
                     fp.write = raise_OSError
                     return fp
 
-                with support.swap_attr(io, "open", bad_writer):
+                with support.swap_attr(io, "open", bad_writer) as orig_open:
                     # test again with failing write()
                     with self.assertRaises(IOError) as cm:
                         tempfile._get_default_tempdir()
diff --git a/Misc/NEWS b/Misc/NEWS
index 657b2fb84e1305..8ec9f2a0eb167b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -144,6 +144,12 @@ Build
 Tests
 -----
 
+- bpo-30197: Enhanced function swap_attr() in the test.test_support module.
+  It now works when delete replaced attribute inside the with statement.  The
+  old value of the attribute (or None if it doesn't exist) now will be
+  assigned to the target of the "as" clause, if there is one.
+  Also backported function swap_item().
+
 - bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS.
   Skip some tests of select.poll when running on macOS due to unresolved
   issues with the underlying system poll function on some macOS versions.

From aa73f409e5f199fcb7d8e3effedc1cf0411a13a2 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 28 Apr 2017 19:45:41 +0300
Subject: [PATCH 2/2] [2.7] bpo-30197: Enhance functions swap_attr() and
 swap_item() in test.support. (GH-1341)

* bpo-30197: Enhance functions swap_attr() and swap_item() in test.support.

They now work when delete replaced attribute or item inside the with
statement.  The old value of the attribute or item (or None if it doesn't
exist) now will be assigned to the target of the "as" clause, if there is
one.

* Update docstrings..
(cherry picked from commit d1a1def7bf221b04dcf3fc3a67aa19aa2f622f83)