bpo-41287: Handle doc argument of property.__init__ in subclasses (#23205)

Fixes #85459

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Lib/test/test_property.py

@@ -219,6 +219,9 @@ class PropertyTests(unittest.TestCase):
 class PropertySub(property):
     """This is a subclass of property"""
 
+class PropertySubWoDoc(property):
+    pass
+
 class PropertySubSlots(property):
     """This is a subclass of property that defines __slots__"""
     __slots__ = ()
@@ -237,6 +240,38 @@ class PropertySubclassTests(unittest.TestCase):
         else:
             raise Exception("AttributeError not raised")
 
+    @unittest.skipIf(sys.flags.optimize >= 2,
+                     "Docstrings are omitted with -O2 and above")
+    def test_issue41287(self):
+
+        self.assertEqual(PropertySub.__doc__, "This is a subclass of property",
+                         "Docstring of `property` subclass is ignored")
+
+        doc = PropertySub(None, None, None, "issue 41287 is fixed").__doc__
+        self.assertEqual(doc, "issue 41287 is fixed",
+                         "Subclasses of `property` ignores `doc` constructor argument")
+
+        def getter(x):
+            """Getter docstring"""
+
+        def getter_wo_doc(x):
+            pass
+
+        for ps in property, PropertySub, PropertySubWoDoc:
+            doc = ps(getter, None, None, "issue 41287 is fixed").__doc__
+            self.assertEqual(doc, "issue 41287 is fixed",
+                             "Getter overrides explicit property docstring (%s)" % ps.__name__)
+
+            doc = ps(getter, None, None, None).__doc__
+            self.assertEqual(doc, "Getter docstring", "Getter docstring is not picked-up (%s)" % ps.__name__)
+
+            doc = ps(getter_wo_doc, None, None, "issue 41287 is fixed").__doc__
+            self.assertEqual(doc, "issue 41287 is fixed",
+                             "Getter overrides explicit property docstring (%s)" % ps.__name__)
+
+            doc = ps(getter_wo_doc, None, None, None).__doc__
+            self.assertIsNone(doc, "Property class doc appears in instance __doc__ (%s)" % ps.__name__)
+
     @unittest.skipIf(sys.flags.optimize >= 2,
                      "Docstrings are omitted with -O2 and above")
     def test_docstring_copy(self):
@@ -249,6 +284,66 @@ class PropertySubclassTests(unittest.TestCase):
             Foo.spam.__doc__,
             "spam wrapped in property subclass")
 
+    @unittest.skipIf(sys.flags.optimize >= 2,
+                     "Docstrings are omitted with -O2 and above")
+    def test_docstring_copy2(self):
+        """
+        Property tries to provide the best docstring it finds for its instances.
+        If a user-provided docstring is available, it is preserved on copies.
+        If no docstring is available during property creation, the property
+        will utilize the docstring from the getter if available.
+        """
+        def getter1(self):
+            return 1
+        def getter2(self):
+            """doc 2"""
+            return 2
+        def getter3(self):
+            """doc 3"""
+            return 3
+
+        # Case-1: user-provided doc is preserved in copies
+        #         of property with undocumented getter
+        p = property(getter1, None, None, "doc-A")
+
+        p2 = p.getter(getter2)
+        self.assertEqual(p.__doc__, "doc-A")
+        self.assertEqual(p2.__doc__, "doc-A")
+
+        # Case-2: user-provided doc is preserved in copies
+        #         of property with documented getter
+        p = property(getter2, None, None, "doc-A")
+
+        p2 = p.getter(getter3)
+        self.assertEqual(p.__doc__, "doc-A")
+        self.assertEqual(p2.__doc__, "doc-A")
+
+        # Case-3: with no user-provided doc new getter doc
+        #         takes precendence
+        p = property(getter2, None, None, None)
+
+        p2 = p.getter(getter3)
+        self.assertEqual(p.__doc__, "doc 2")
+        self.assertEqual(p2.__doc__, "doc 3")
+
+        # Case-4: A user-provided doc is assigned after property construction
+        #         with documented getter. The doc IS NOT preserved.
+        #         It's an odd behaviour, but it's a strange enough
+        #         use case with no easy solution.
+        p = property(getter2, None, None, None)
+        p.__doc__ = "user"
+        p2 = p.getter(getter3)
+        self.assertEqual(p.__doc__, "user")
+        self.assertEqual(p2.__doc__, "doc 3")
+
+        # Case-5: A user-provided doc is assigned after property construction
+        #         with UNdocumented getter. The doc IS preserved.
+        p = property(getter1, None, None, None)
+        p.__doc__ = "user"
+        p2 = p.getter(getter2)
+        self.assertEqual(p.__doc__, "user")
+        self.assertEqual(p2.__doc__, "user")
+
     @unittest.skipIf(sys.flags.optimize >= 2,
                      "Docstrings are omitted with -O2 and above")
     def test_property_setter_copies_getter_docstring(self):