Feedback from Petr

Author: JelleZijlstra

Lib/dataclasses.py

@@ -1283,6 +1283,10 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
     if '__slots__' in cls.__dict__:
         raise TypeError(f'{cls.__name__} already specifies __slots__')
 
+    # gh-102069: Remove existing __weakref__ descriptor.
+    # gh-135228: Make sure the original class can be garbage collected.
+    sys._clear_type_descriptors(cls)
+
     # Create a new dict for our new class.
     cls_dict = dict(cls.__dict__)
     field_names = tuple(f.name for f in fields(cls))
@@ -1300,12 +1304,6 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
         #  available in _MARKER.
         cls_dict.pop(field_name, None)
 
-    # Remove __dict__ itself.
-    cls_dict.pop('__dict__', None)
-
-    # Clear existing `__weakref__` descriptor, it belongs to a previous type:
-    cls_dict.pop('__weakref__', None)  # gh-102069
-
     # And finally create the class.
     qualname = getattr(cls, '__qualname__', None)
     newcls = type(cls)(cls.__name__, cls.__bases__, cls_dict)
@@ -1338,9 +1336,6 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
                 or _update_func_cell_for__class__(member.fdel, cls, newcls)):
                 break
 
-    # gh-135228: Make sure the original class can be garbage collected.
-    sys._clear_type_descriptors(cls)
-
     return newcls
 
 

Misc/NEWS.d/next/Library/2025-07-20-16-56-55.gh-issue-135228.n_XIao.rst

@@ -1,4 +1,4 @@
 When :mod:`dataclasses` replaces a class with a slotted dataclass, the
-original class is now garbage collected again. Earlier changes in Python
-3.14 caused this class to remain in existence together with the replacement
+original class can now be garbage collected again. Earlier changes in Python
+3.14 caused this class to always remain in existence together with the replacement
 class synthesized by :mod:`dataclasses`.