From: Serhiy Storchaka <storchaka@gmail.com>
Date: Fri, 28 Apr 2017 17:05:05 +0000 (+0300)
Subject: [3.6] bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. ... 
X-Git-Tag: v3.6.2rc1~192
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=712114b3f9f5f98f03c66a80607b6f7101c5cc90;p=python

[3.6] bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. (GH-1341) (#1345)

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.

(cherry picked from commit d1a1def7bf221b04dcf3fc3a67aa19aa2f622f83)
---

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 2d60adc3dc..f8d177990b 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -2105,12 +2105,15 @@ 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:
@@ -2118,7 +2121,8 @@ 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):
@@ -2132,12 +2136,15 @@ def swap_item(obj, item, new_val):
         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
+            yield real_val
         finally:
             obj[item] = real_val
     else:
@@ -2145,7 +2152,8 @@ def swap_item(obj, item, new_val):
         try:
             yield
         finally:
-            del obj[item]
+            if item in obj:
+                del obj[item]
 
 def strip_python_stderr(stderr):
     """Strip the stderr of a Python process from potential debug output
diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index e83a4d6426..ddd6509231 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -282,17 +282,34 @@ class TestSupport(unittest.TestCase):
 
     def test_swap_attr(self):
         class Obj:
-            x = 1
+            pass
         obj = Obj()
-        with support.swap_attr(obj, "x", 5):
+        obj.x = 1
+        with support.swap_attr(obj, "x", 5) as x:
             self.assertEqual(obj.x, 5)
+            self.assertEqual(x, 1)
         self.assertEqual(obj.x, 1)
+        with support.swap_attr(obj, "y", 5) as y:
+            self.assertEqual(obj.y, 5)
+            self.assertIsNone(y)
+        self.assertFalse(hasattr(obj, 'y'))
+        with support.swap_attr(obj, "y", 5):
+            del obj.y
+        self.assertFalse(hasattr(obj, 'y'))
 
     def test_swap_item(self):
-        D = {"item":1}
-        with support.swap_item(D, "item", 5):
-            self.assertEqual(D["item"], 5)
-        self.assertEqual(D["item"], 1)
+        D = {"x":1}
+        with support.swap_item(D, "x", 5) as x:
+            self.assertEqual(D["x"], 5)
+            self.assertEqual(x, 1)
+        self.assertEqual(D["x"], 1)
+        with support.swap_item(D, "y", 5) as y:
+            self.assertEqual(D["y"], 5)
+            self.assertIsNone(y)
+        self.assertNotIn("y", D)
+        with support.swap_item(D, "y", 5):
+            del D["y"]
+        self.assertNotIn("y", D)
 
     class RefClass:
         attribute1 = None
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 51df1ecd7d..d0cf04b0cb 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -273,13 +273,12 @@ class TestGetDefaultTempdir(BaseTestCase):
                         tempfile._get_default_tempdir()
                     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(FileNotFoundError):
                         tempfile._get_default_tempdir()
diff --git a/Misc/NEWS b/Misc/NEWS
index b1f79d6124..936e2b0201 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -114,6 +114,15 @@ Documentation
 
 - bpo-26985: Add missing info of code object in inspect documentation.
 
+Tests
+-----
+
+- bpo-30197: Enhanced functions swap_attr() and swap_item() in the
+  test.support module.  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.
+
 
 What's New in Python 3.6.1?
 ===========================