bpo-33175: dataclasses should look up __set_name__ on class, not instance (GH-6305)
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@ -248,11 +248,11 @@ class Field:
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# the default value, so the end result is a descriptor that had
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# __set_name__ called on it at the right time.
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def __set_name__(self, owner, name):
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func = getattr(self.default, '__set_name__', None)
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func = getattr(type(self.default), '__set_name__', None)
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if func:
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# There is a __set_name__ method on the descriptor,
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# call it.
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func(owner, name)
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func(self.default, owner, name)
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class _DataclassParams:
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@ -2705,7 +2705,7 @@ class TestDescriptors(unittest.TestCase):
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# Create a descriptor.
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class D:
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def __set_name__(self, owner, name):
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self.name = name
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self.name = name + 'x'
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def __get__(self, instance, owner):
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if instance is not None:
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return 1
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@ -2716,7 +2716,7 @@ class TestDescriptors(unittest.TestCase):
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@dataclass
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class C:
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c: int=D()
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self.assertEqual(C.c.name, 'c')
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self.assertEqual(C.c.name, 'cx')
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# Now test with a default value and init=False, which is the
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# only time this is really meaningful. If not using
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@ -2724,7 +2724,7 @@ class TestDescriptors(unittest.TestCase):
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@dataclass
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class C:
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c: int=field(default=D(), init=False)
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self.assertEqual(C.c.name, 'c')
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self.assertEqual(C.c.name, 'cx')
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self.assertEqual(C().c, 1)
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def test_non_descriptor(self):
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@ -2733,12 +2733,41 @@ class TestDescriptors(unittest.TestCase):
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class D:
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def __set_name__(self, owner, name):
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self.name = name
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self.name = name + 'x'
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@dataclass
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class C:
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c: int=field(default=D(), init=False)
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self.assertEqual(C.c.name, 'c')
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self.assertEqual(C.c.name, 'cx')
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def test_lookup_on_instance(self):
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# See bpo-33175.
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class D:
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pass
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d = D()
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# Create an attribute on the instance, not type.
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d.__set_name__ = Mock()
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# Make sure d.__set_name__ is not called.
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@dataclass
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class C:
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i: int=field(default=d, init=False)
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self.assertEqual(d.__set_name__.call_count, 0)
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def test_lookup_on_class(self):
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# See bpo-33175.
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class D:
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pass
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D.__set_name__ = Mock()
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# Make sure D.__set_name__ is called.
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@dataclass
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class C:
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i: int=field(default=D(), init=False)
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self.assertEqual(D.__set_name__.call_count, 1)
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if __name__ == '__main__':
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@ -0,0 +1,2 @@
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In dataclasses, Field.__set_name__ now looks up the __set_name__ special
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method on the class, not the instance, of the default value.
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