Detect line numbers for cached properties in doctests

Author: dlax

Lib/doctest.py

@@ -94,6 +94,7 @@ def _test():
 
 import __future__
 import difflib
+import functools
 import inspect
 import linecache
 import os
@@ -1141,6 +1142,8 @@ def _find_lineno(self, obj, source_lines):
         if inspect.ismethod(obj): obj = obj.__func__
         if isinstance(obj, property):
             obj = obj.fget
+        if isinstance(obj, functools.cached_property):
+            obj = obj.func
         if inspect.isroutine(obj) and getattr(obj, '__doc__', None):
             # We don't use `docstring` var here, because `obj` can be changed.
             obj = inspect.unwrap(obj)

Lib/test/test_doctest/doctest_lineno.py

@@ -94,3 +94,14 @@ def cached_func_with_doctest(value):
 @functools.cache
 def cached_func_without_docstring(value):
     return value + 1
+
+
+class ClassWithACachedProperty:
+
+    @functools.cached_property
+    def cached(self):
+        """
+        >>> X().cached
+        -1
+        """
+        return 0

Lib/test/test_doctest/test_doctest.py

@@ -678,6 +678,8 @@ def basics(): r"""
     >>> for t in tests:
     ...     print('%5s  %s' % (t.lineno, t.name))
      None  test.test_doctest.doctest_lineno
+     None  test.test_doctest.doctest_lineno.ClassWithACachedProperty
+      102  test.test_doctest.doctest_lineno.ClassWithACachedProperty.cached
        22  test.test_doctest.doctest_lineno.ClassWithDocstring
        30  test.test_doctest.doctest_lineno.ClassWithDoctest
      None  test.test_doctest.doctest_lineno.ClassWithoutDocstring

Misc/NEWS.d/next/Library/2025-07-21-15-40-00.gh-issue-136914.-GNG-d.rst

@@ -1 +1,2 @@
-Fix retrieval of :attr:`doctest.DocTest.lineno` for :func:`functools.cache`-decorated functions.
+Fix retrieval of :attr:`doctest.DocTest.lineno` for objects decorated with
+:func:`functools.cache` or :class:`functools.cached_property`.