gh-102578: Optimise setting and deleting mutable attributes on non-dataclass subclasses of frozen dataclasses (gh-102573)

1 files changed, 4 insertions, 6 deletions

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 8bc8594..78a126f 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -616,21 +616,19 @@ def _repr_fn(fields, globals):
 def _frozen_get_del_attr(cls, fields, globals):
     locals = {'cls': cls,
               'FrozenInstanceError': FrozenInstanceError}
+    condition = 'type(self) is cls'
     if fields:
-        fields_str = '(' + ','.join(repr(f.name) for f in fields) + ',)'
-    else:
-        # Special case for the zero-length tuple.
-        fields_str = '()'
+        condition += ' or name in {' + ', '.join(repr(f.name) for f in fields) + '}'
     return (_create_fn('__setattr__',
                       ('self', 'name', 'value'),
-                      (f'if type(self) is cls or name in {fields_str}:',
+                      (f'if {condition}:',
                         ' raise FrozenInstanceError(f"cannot assign to field {name!r}")',
                        f'super(cls, self).__setattr__(name, value)'),
                        locals=locals,
                        globals=globals),
             _create_fn('__delattr__',
                       ('self', 'name'),
-                      (f'if type(self) is cls or name in {fields_str}:',
+                      (f'if {condition}:',
                         ' raise FrozenInstanceError(f"cannot delete field {name!r}")',
                        f'super(cls, self).__delattr__(name)'),
                        locals=locals,