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

Patch contributed by Sean McCully.

NEWS

diff --git a/NEWS b/NEWS
index 5e91ac8..2e13b8a 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,9 @@
 Library
 -------
 
+- Issue #22138: Fix mock.patch behavior when patching descriptors. Restore
+  original values after patching. Patch contributed by Sean McCully.
+
 - Issue #24857: Comparing call_args to a long sequence now correctly returns a
   boolean result instead of raising an exception.  Patch by A Kaptur.
 

mock/mock.py

diff --git a/mock/mock.py b/mock/mock.py
index 4846a46..8174766 100644
--- a/mock/mock.py
+++ b/mock/mock.py
@@ -1477,7 +1477,10 @@
             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)
 

mock/tests/testpatch.py

diff --git a/mock/tests/testpatch.py b/mock/tests/testpatch.py
index 761ce99..32a6c27 100644
--- a/mock/tests/testpatch.py
+++ b/mock/tests/testpatch.py
@@ -1852,5 +1852,32 @@
         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__, __name__)
+
+        if hasattr(self.test_special_attrs, '__annotations__'):
+            with patch.object(foo, '__annotations__', dict([('s', 1, )])):
+                self.assertEqual(foo.__annotations__, dict([('s', 1, )]))
+            self.assertEqual(foo.__annotations__, dict())
+
+        if hasattr(self.test_special_attrs, '__kwdefaults__'):
+            foo = eval("lambda *a, x=0: x")
+            with patch.object(foo, '__kwdefaults__', dict([('x', 1, )])):
+                self.assertEqual(foo(), 1)
+            self.assertEqual(foo(), 0)
+
 if __name__ == '__main__':
     unittest.main()