bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867)
Co-Authored-By: Claudiu Popa <pcmanticore@gmail.com>
Automerge-Triggered-By: GH:ericvsmith
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 422a95c..3de2ec0 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -1300,7 +1300,7 @@ class C:
continue
if f.name not in changes:
- if f._field_type is _FIELD_INITVAR:
+ if f._field_type is _FIELD_INITVAR and f.default is MISSING:
raise ValueError(f"InitVar {f.name!r} "
'must be specified with replace()')
changes[f.name] = getattr(obj, f.name)
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 0bfed41..4f5c3c8 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3251,6 +3251,24 @@ def __post_init__(self, y):
c = replace(c, x=3, y=5)
self.assertEqual(c.x, 15)
+ def test_initvar_with_default_value(self):
+ @dataclass
+ class C:
+ x: int
+ y: InitVar[int] = None
+ z: InitVar[int] = 42
+
+ def __post_init__(self, y, z):
+ if y is not None:
+ self.x += y
+ if z is not None:
+ self.x += z
+
+ c = C(x=1, y=10, z=1)
+ self.assertEqual(replace(c), C(x=12))
+ self.assertEqual(replace(c, y=4), C(x=12, y=4, z=42))
+ self.assertEqual(replace(c, y=4, z=1), C(x=12, y=4, z=1))
+
def test_recursive_repr(self):
@dataclass
class C: