From d3062f672c92855b7e9e962ad4bf1a67abd4589b Mon Sep 17 00:00:00 2001 From: "Eric V. Smith" Date: Mon, 22 Nov 2021 08:26:12 -0500 Subject: bpo-44649: Fix dataclasses(slots=True) with a field with a default, but init=False (GH-29692) Special handling is needed, because for non-slots dataclasses the instance attributes are not set: reading from a field just references the class's attribute of the same name, which contains the default value. But this doesn't work for classes using __slots__: they don't read the class's attribute. So in that case (and that case only), initialize the instance attribute. Handle this for both normal defaults, and for fields using default_factory. --- Lib/test/test_dataclasses.py | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'Lib/test/test_dataclasses.py') diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py index b00d0484d3..bcd004f4ec 100644 --- a/Lib/test/test_dataclasses.py +++ b/Lib/test/test_dataclasses.py @@ -2880,6 +2880,28 @@ class TestSlots(unittest.TestCase): self.assertIsNot(obj, p) self.assertEqual(obj, p) + def test_slots_with_default_no_init(self): + # Originally reported in bpo-44649. + @dataclass(slots=True) + class A: + a: str + b: str = field(default='b', init=False) + + obj = A("a") + self.assertEqual(obj.a, 'a') + self.assertEqual(obj.b, 'b') + + def test_slots_with_default_factory_no_init(self): + # Originally reported in bpo-44649. + @dataclass(slots=True) + class A: + a: str + b: str = field(default_factory=lambda:'b', init=False) + + obj = A("a") + self.assertEqual(obj.a, 'a') + self.assertEqual(obj.b, 'b') + class TestDescriptors(unittest.TestCase): def test_set_name(self): # See bpo-33141. -- cgit v1.2.1