bpo-44904: Fix classmethod property bug in doctest module (GH-28838)

The doctest module raised an error if a docstring contained an example that
attempted to access a classmethod property. (Stacking '@classmethod' on top of
`@property` has been supported since Python 3.9; see
https://docs.python.org/3/howto/descriptor.htmlGH-class-methods.)

Co-authored-by: Serhiy Storchaka <[email protected]>
(cherry picked from commit b1302ab)

Co-authored-by: Alex Waygood <[email protected]>

Author: miss-islington

Lib/doctest.py

@@ -1022,10 +1022,8 @@ def _find(self, tests, obj, name, module, source_lines, globs, seen):
         if inspect.isclass(obj) and self._recurse:
             for valname, val in obj.__dict__.items():
                 # Special handling for staticmethod/classmethod.
-                if isinstance(val, staticmethod):
-                    val = getattr(obj, valname)
-                if isinstance(val, classmethod):
-                    val = getattr(obj, valname).__func__
+                if isinstance(val, (staticmethod, classmethod)):
+                    val = val.__func__
 
                 # Recurse to methods, properties, and nested classes.
                 if ((inspect.isroutine(val) or inspect.isclass(val) or

Lib/test/test_doctest.py

@@ -93,6 +93,17 @@ def a_classmethod(cls, v):
         22
         """)
 
+    a_class_attribute = 42
+
+    @classmethod
+    @property
+    def a_classmethod_property(cls):
+        """
+        >>> print(SampleClass.a_classmethod_property)
+        42
+        """
+        return cls.a_class_attribute
+
     class NestedClass:
         """
         >>> x = SampleClass.NestedClass(5)
@@ -498,6 +509,7 @@ def basics(): r"""
      1  SampleClass.NestedClass.__init__
      1  SampleClass.__init__
      2  SampleClass.a_classmethod
+     1  SampleClass.a_classmethod_property
      1  SampleClass.a_property
      1  SampleClass.a_staticmethod
      1  SampleClass.double
@@ -553,6 +565,7 @@ def basics(): r"""
      1  some_module.SampleClass.NestedClass.__init__
      1  some_module.SampleClass.__init__
      2  some_module.SampleClass.a_classmethod
+     1  some_module.SampleClass.a_classmethod_property
      1  some_module.SampleClass.a_property
      1  some_module.SampleClass.a_staticmethod
      1  some_module.SampleClass.double
@@ -594,6 +607,7 @@ def basics(): r"""
      1  SampleClass.NestedClass.__init__
      1  SampleClass.__init__
      2  SampleClass.a_classmethod
+     1  SampleClass.a_classmethod_property
      1  SampleClass.a_property
      1  SampleClass.a_staticmethod
      1  SampleClass.double
@@ -614,6 +628,7 @@ def basics(): r"""
      0  SampleClass.NestedClass.square
      1  SampleClass.__init__
      2  SampleClass.a_classmethod
+     1  SampleClass.a_classmethod_property
      1  SampleClass.a_property
      1  SampleClass.a_staticmethod
      1  SampleClass.double

Misc/ACKS

@@ -1846,6 +1846,7 @@ Bob Watson
 Colin Watson
 David Watson
 Aaron Watters
+Alex Waygood
 Henrik Weber
 Leon Weber
 Steve Weber

Misc/NEWS.d/next/Library/2021-10-09-18-42-27.bpo-44904.RlW5h8.rst

@@ -0,0 +1,3 @@
+Fix bug in the :mod:`doctest` module that caused it to fail if a docstring
+included an example with a ``classmethod`` ``property``. Patch by Alex
+Waygood.