Issue #22138: Fix mock.patch behavior when patching descriptors. Restore

original values after patching.

Patch contributed by Sean McCully.

Lib/unittest/mock.py

@@ -1332,7 +1332,10 @@ class _patch(object):
             setattr(self.target, self.attribute, self.temp_original)
         else:
             delattr(self.target, self.attribute)
-            if not self.create and not hasattr(self.target, self.attribute):
+            if not self.create and (not hasattr(self.target, self.attribute) or
+                        self.attribute in ('__doc__', '__module__',
+                                           '__defaults__', '__annotations__',
+                                           '__kwdefaults__')):
                 # needed for proxy objects like django settings
                 setattr(self.target, self.attribute, self.temp_original)
 

Lib/unittest/test/testmock/testpatch.py

@@ -1817,5 +1817,31 @@ class PatchTest(unittest.TestCase):
         self.assertEqual(stopped, ["three", "two", "one"])
 
 
+    def test_special_attrs(self):
+        def foo(x=0):
+            """TEST"""
+            return x
+        with patch.object(foo, '__defaults__', (1, )):
+            self.assertEqual(foo(), 1)
+        self.assertEqual(foo(), 0)
+
+        with patch.object(foo, '__doc__', "FUN"):
+            self.assertEqual(foo.__doc__, "FUN")
+        self.assertEqual(foo.__doc__, "TEST")
+
+        with patch.object(foo, '__module__', "testpatch2"):
+            self.assertEqual(foo.__module__, "testpatch2")
+        self.assertEqual(foo.__module__, 'unittest.test.testmock.testpatch')
+
+        with patch.object(foo, '__annotations__', dict([('s', 1, )])):
+            self.assertEqual(foo.__annotations__, dict([('s', 1, )]))
+        self.assertEqual(foo.__annotations__, dict())
+
+        def foo(*a, x=0):
+            return x
+        with patch.object(foo, '__kwdefaults__', dict([('x', 1, )])):
+            self.assertEqual(foo(), 1)
+        self.assertEqual(foo(), 0)
+
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS

@@ -41,6 +41,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #22138: Fix mock.patch behavior when patching descriptors. Restore
+  original values after patching. Patch contributed by Sean McCully.
+
 - Issue #25672: In the ssl module, enable the SSL_MODE_RELEASE_BUFFERS mode
   option if it is safe to do so.