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Commitee6f841

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gh-102578: Optimise setting and deleting mutable attributes on non-dataclass subclasses of frozen dataclasses (gh-102573)
1 parent90f1d77 commitee6f841

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3 files changed

+52
-6
lines changed

3 files changed

+52
-6
lines changed

‎Lib/dataclasses.py‎

Lines changed: 4 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -616,21 +616,19 @@ def _repr_fn(fields, globals):
616616
def_frozen_get_del_attr(cls,fields,globals):
617617
locals= {'cls':cls,
618618
'FrozenInstanceError':FrozenInstanceError}
619+
condition='type(self) is cls'
619620
iffields:
620-
fields_str='('+','.join(repr(f.name)forfinfields)+',)'
621-
else:
622-
# Special case for the zero-length tuple.
623-
fields_str='()'
621+
condition+=' or name in {'+', '.join(repr(f.name)forfinfields)+'}'
624622
return (_create_fn('__setattr__',
625623
('self','name','value'),
626-
(f'iftype(self) is cls or name in{fields_str}:',
624+
(f'if{condition}:',
627625
' raise FrozenInstanceError(f"cannot assign to field {name!r}")',
628626
f'super(cls, self).__setattr__(name, value)'),
629627
locals=locals,
630628
globals=globals),
631629
_create_fn('__delattr__',
632630
('self','name'),
633-
(f'iftype(self) is cls or name in{fields_str}:',
631+
(f'if{condition}:',
634632
' raise FrozenInstanceError(f"cannot delete field {name!r}")',
635633
f'super(cls, self).__delattr__(name)'),
636634
locals=locals,

‎Lib/test/test_dataclasses.py‎

Lines changed: 44 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2767,6 +2767,19 @@ class C:
27672767
c.i=5
27682768
self.assertEqual(c.i,10)
27692769

2770+
deftest_frozen_empty(self):
2771+
@dataclass(frozen=True)
2772+
classC:
2773+
pass
2774+
2775+
c=C()
2776+
self.assertFalse(hasattr(c,'i'))
2777+
withself.assertRaises(FrozenInstanceError):
2778+
c.i=5
2779+
self.assertFalse(hasattr(c,'i'))
2780+
withself.assertRaises(FrozenInstanceError):
2781+
delc.i
2782+
27702783
deftest_inherit(self):
27712784
@dataclass(frozen=True)
27722785
classC:
@@ -2890,6 +2903,37 @@ class S(D):
28902903
self.assertEqual(s.y,10)
28912904
self.assertEqual(s.cached,True)
28922905

2906+
withself.assertRaises(FrozenInstanceError):
2907+
dels.x
2908+
self.assertEqual(s.x,3)
2909+
withself.assertRaises(FrozenInstanceError):
2910+
dels.y
2911+
self.assertEqual(s.y,10)
2912+
dels.cached
2913+
self.assertFalse(hasattr(s,'cached'))
2914+
withself.assertRaises(AttributeError)ascm:
2915+
dels.cached
2916+
self.assertNotIsInstance(cm.exception,FrozenInstanceError)
2917+
2918+
deftest_non_frozen_normal_derived_from_empty_frozen(self):
2919+
@dataclass(frozen=True)
2920+
classD:
2921+
pass
2922+
2923+
classS(D):
2924+
pass
2925+
2926+
s=S()
2927+
self.assertFalse(hasattr(s,'x'))
2928+
s.x=5
2929+
self.assertEqual(s.x,5)
2930+
2931+
dels.x
2932+
self.assertFalse(hasattr(s,'x'))
2933+
withself.assertRaises(AttributeError)ascm:
2934+
dels.x
2935+
self.assertNotIsInstance(cm.exception,FrozenInstanceError)
2936+
28932937
deftest_overwriting_frozen(self):
28942938
# frozen uses __setattr__ and __delattr__.
28952939
withself.assertRaisesRegex(TypeError,
Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,4 @@
1+
Speed up setting or deleting mutable attributes on non-dataclass subclasses of
2+
frozen dataclasses. Due to the implementation of ``__setattr__`` and
3+
``__delattr__`` for frozen dataclasses, this previously had a time complexity
4+
of ``O(n)``. It now has a time complexity of ``O(1)``.

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