Document and test the resolution of issue 3445 (tolerate missing attributes in functools.update_wrapper, previously implemented as a side effect of the __annotations__ copying patch) and implement issue 9567 (add a __wrapped__ attribute when using update_wrapper)

2 files changed, 36 insertions, 2 deletions

diff --git a/Lib/functools.py b/Lib/functools.py
index c2c2282..bd1334b 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -38,9 +38,14 @@ def update_wrapper(wrapper,
        are updated with the corresponding attribute from the wrapped
        function (defaults to functools.WRAPPER_UPDATES)
     """
+    wrapper.__wrapped__ = wrapped
     for attr in assigned:
-        if hasattr(wrapped, attr):
-            setattr(wrapper, attr, getattr(wrapped, attr))
+        try:
+            value = getattr(wrapped, attr)
+        except AttributeError:
+            pass
+        else:
+            setattr(wrapper, attr, value)
     for attr in updated:
         getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
     # Return the wrapper so this can be used as a decorator via partial()
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 2b6da64..211ef18 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -194,6 +194,7 @@ class TestUpdateWrapper(unittest.TestCase):
     def test_default_update(self):
         wrapper, f = self._default_update()
         self.check_wrapper(wrapper, f)
+        self.assertIs(wrapper.__wrapped__, f)
         self.assertEqual(wrapper.__name__, 'f')
         self.assertEqual(wrapper.attr, 'This is also a test')
         self.assertEqual(wrapper.__annotations__['a'], 'This is a new annotation')
@@ -236,6 +237,28 @@ class TestUpdateWrapper(unittest.TestCase):
         self.assertEqual(wrapper.attr, 'This is a different test')
         self.assertEqual(wrapper.dict_attr, f.dict_attr)
 
+    def test_missing_attributes(self):
+        def f():
+            pass
+        def wrapper():
+            pass
+        wrapper.dict_attr = {}
+        assign = ('attr',)
+        update = ('dict_attr',)
+        # Missing attributes on wrapped object are ignored
+        functools.update_wrapper(wrapper, f, assign, update)
+        self.assertNotIn('attr', wrapper.__dict__)
+        self.assertEqual(wrapper.dict_attr, {})
+        # Wrapper must have expected attributes for updating
+        del wrapper.dict_attr
+        with self.assertRaises(AttributeError):
+            functools.update_wrapper(wrapper, f, assign, update)
+        wrapper.dict_attr = 1
+        with self.assertRaises(AttributeError):
+            functools.update_wrapper(wrapper, f, assign, update)
+
+    @unittest.skipIf(sys.flags.optimize >= 2,
+                     "Docstrings are omitted with -O2 and above")
     def test_builtin_update(self):
         # Test for bug #1576241
         def wrapper():
@@ -495,6 +518,12 @@ class TestLRU(unittest.TestCase):
         self.assertEqual(f.hits, 0)
         self.assertEqual(f.misses, 1)
 
+        # Test bypassing the cache
+        self.assertIs(f.__wrapped__, orig)
+        f.__wrapped__(x, y)
+        self.assertEqual(f.hits, 0)
+        self.assertEqual(f.misses, 1)
+
         # test size zero (which means "never-cache")
         @functools.lru_cache(0)
         def f():