bpo-33100: Dataclasses now handles __slots__ and default values correctly. (GH-6152) (GH-6153)
If the class has a member that's a MemberDescriptorType, it's not a default value, it's from that member being in __slots__.
(cherry picked from commit 7389fd935c95b4b6f094312294e703ee0de18719)
Co-authored-by: Eric V. Smith <ericvsmith@users.noreply.github.com>
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 3e67263..db03ec1 100755
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -2564,5 +2564,47 @@
self.assertEqual(s.cached, True)
+class TestSlots(unittest.TestCase):
+ def test_simple(self):
+ @dataclass
+ class C:
+ __slots__ = ('x',)
+ x: Any
+
+ # There was a bug where a variable in a slot was assumed
+ # to also have a default value (of type types.MemberDescriptorType).
+ with self.assertRaisesRegex(TypeError,
+ "__init__\(\) missing 1 required positional argument: 'x'"):
+ C()
+
+ # We can create an instance, and assign to x.
+ c = C(10)
+ self.assertEqual(c.x, 10)
+ c.x = 5
+ self.assertEqual(c.x, 5)
+
+ # We can't assign to anything else.
+ with self.assertRaisesRegex(AttributeError, "'C' object has no attribute 'y'"):
+ c.y = 5
+
+ def test_derived_added_field(self):
+ # See bpo-33100.
+ @dataclass
+ class Base:
+ __slots__ = ('x',)
+ x: Any
+
+ @dataclass
+ class Derived(Base):
+ x: int
+ y: int
+
+ d = Derived(1, 2)
+ self.assertEqual((d.x, d.y), (1, 2))
+
+ # We can add a new field to the derived instance.
+ d.z = 10
+
+
if __name__ == '__main__':
unittest.main()