bpo-44015: dataclasses should allow KW_ONLY to be specified only once per class (GH-25841)
bpo-44015: Raise a TypeError if KW_ONLY is specified more than once.
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 16ee4c7..8e645ae 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3699,6 +3699,83 @@ class C:
self.assertEqual(c.b, 3)
self.assertEqual(c.c, 2)
+ def test_KW_ONLY_as_string(self):
+ @dataclass
+ class A:
+ a: int
+ _: 'dataclasses.KW_ONLY'
+ b: int
+ c: int
+ A(3, c=5, b=4)
+ msg = "takes 2 positional arguments but 4 were given"
+ with self.assertRaisesRegex(TypeError, msg):
+ A(3, 4, 5)
+
+ def test_KW_ONLY_twice(self):
+ msg = "'Y' is KW_ONLY, but KW_ONLY has already been specified"
+
+ with self.assertRaisesRegex(TypeError, msg):
+ @dataclass
+ class A:
+ a: int
+ X: KW_ONLY
+ Y: KW_ONLY
+ b: int
+ c: int
+
+ with self.assertRaisesRegex(TypeError, msg):
+ @dataclass
+ class A:
+ a: int
+ X: KW_ONLY
+ b: int
+ Y: KW_ONLY
+ c: int
+
+ with self.assertRaisesRegex(TypeError, msg):
+ @dataclass
+ class A:
+ a: int
+ X: KW_ONLY
+ b: int
+ c: int
+ Y: KW_ONLY
+
+ # But this usage is okay, since it's not using KW_ONLY.
+ @dataclass
+ class A:
+ a: int
+ _: KW_ONLY
+ b: int
+ c: int = field(kw_only=True)
+
+ # And if inheriting, it's okay.
+ @dataclass
+ class A:
+ a: int
+ _: KW_ONLY
+ b: int
+ c: int
+ @dataclass
+ class B(A):
+ _: KW_ONLY
+ d: int
+
+ # Make sure the error is raised in a derived class.
+ with self.assertRaisesRegex(TypeError, msg):
+ @dataclass
+ class A:
+ a: int
+ _: KW_ONLY
+ b: int
+ c: int
+ @dataclass
+ class B(A):
+ X: KW_ONLY
+ d: int
+ Y: KW_ONLY
+
+
def test_post_init(self):
@dataclass
class A: