gh-131116: Fix inspect._finddoc to work with cached_property objects.

Lib/inspect.py

@@ -747,6 +747,12 @@ def _finddoc(obj):
         cls = _findclass(obj.fget)
         if cls is None or getattr(cls, name) is not obj:
             return None
+    # Should be tested before ismethoddescriptor()
+    elif isinstance(obj, functools.cached_property):
+        name = obj.attrname
+        cls = _findclass(obj.func)
+        if cls is None or getattr(cls, name) is not obj:
+            return None
     elif ismethoddescriptor(obj) or isdatadescriptor(obj):
         name = obj.__name__
         cls = obj.__objclass__

Lib/test/test_inspect/inspect_fodder3.py

@@ -0,0 +1,12 @@
+from functools import cached_property
+
+class Parent:
+    @cached_property
+    def foo(self):
+        "this is the docstring for foo"
+        pass
+
+class Child(Parent):
+    @cached_property
+    def foo(self):
+        pass

Lib/test/test_inspect/test_inspect.py

@@ -46,6 +46,7 @@
 
 from test.test_inspect import inspect_fodder as mod
 from test.test_inspect import inspect_fodder2 as mod2
+from test.test_inspect import inspect_fodder3 as mod3
 from test.test_inspect import inspect_stringized_annotations
 from test.test_inspect import inspect_deferred_annotations
 
@@ -665,6 +666,10 @@ def test_getdoc_inherited(self):
         self.assertEqual(inspect.getdoc(mod.FesteringGob.contradiction),
                          'The automatic gainsaying.')
 
+    def test_getdoc_inherited_cached_property(self):
+        self.assertEqual(inspect.getdoc(mod3.Parent.foo),
+                         inspect.getdoc(mod3.Child.foo))
+
     @unittest.skipIf(MISSING_C_DOCSTRINGS, "test requires docstrings")
     def test_finddoc(self):
         finddoc = inspect._finddoc

Misc/NEWS.d/next/Library/2025-03-12-18-57-10.gh-issue-131116.uTpwXZ.rst

@@ -0,0 +1 @@
+inspect.getdoc(), if run on a cached_property that does not define a docstring but inherits from a class that did define a docstring, will now return the inherited docstring rather than None.