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Co-authored-by: Alyssa Coghlan <[email protected]>

Author: JelleZijlstra

Lib/dataclasses.py

@@ -1339,9 +1339,10 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
                 break
 
     # gh-135228: Make sure the original class can be garbage collected.
+    # Bypass mapping proxy to allow __dict__ to be removed
     old_cls_dict = cls.__dict__ | _deproxier
-    old_cls_dict.pop('__weakref__', None)
     old_cls_dict.pop('__dict__', None)
+    del cls.__weakref__
 
     return newcls