gh-140972: Empty docstrings passed to DynamicClassAttribute are preserved

Lib/test/test_dynamicclassattribute.py

@@ -4,6 +4,7 @@
 import abc
 import sys
 import unittest
+from test import support
 from types import DynamicClassAttribute
 
 class PropertyBase(Exception):
@@ -195,6 +196,16 @@ def __init__(self):
             Okay2.color
         self.assertEqual(Okay2().color, 'magenta')
 
+    @support.requires_docstrings
+    def test_empty_docstring(self):
+        attr = DynamicClassAttribute(fget=None, fset=None, fdel=None, doc='')
+        self.assertEqual(attr.__doc__, '')
+        def fget():
+            """fget's docstring"""
+        attr_with_fget = DynamicClassAttribute(fget=fget, doc='')
+        self.assertEqual(attr_with_fget.__doc__, '')
+        attr_no_doc = DynamicClassAttribute(fget=None)
+        self.assertIsNone(attr_no_doc.__doc__)
 
 # Issue 5890: subclasses of DynamicClassAttribute do not preserve method __doc__ strings
 class PropertySub(DynamicClassAttribute):

Lib/types.py

@@ -210,9 +210,12 @@ def __init__(self, fget=None, fset=None, fdel=None, doc=None):
         self.fget = fget
         self.fset = fset
         self.fdel = fdel
+        overwrite_doc = doc is None
+        if doc is None and fget is not None:
+            doc = fget.__doc__
         # next two lines make DynamicClassAttribute act the same as property
-        self.__doc__ = doc or fget.__doc__
-        self.overwrite_doc = doc is None
+        self.__doc__ = doc
+        self.overwrite_doc = overwrite_doc
         # support for abstract methods
         self.__isabstractmethod__ = bool(getattr(fget, '__isabstractmethod__', False))
 

Misc/NEWS.d/next/Library/2025-11-08-21-01-46.gh-issue-140972.v960ZZ.rst

@@ -0,0 +1,3 @@
+Now empty docstrings passed to :func:`types.DynamicClassAttribute` are
+preserved when ``fget`` is ``None``; previously ``NoneType.__doc__`` was used
+incorrectly.