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mauvilsa merged 1 commit into from
Jan 22, 2026
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Union of dataclasses not discarding parameters on class change #833

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2 changes: 2 additions & 0 deletions CHANGELOG.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,8 @@ Fixed
^^^^^
- Choices with an int type not working correctly (`#827
<https://github.com/omni-us/jsonargparse/pull/827>`__).
- Union of dataclasses not discarding parameters on class change (`#833
<https://github.com/omni-us/jsonargparse/pull/833>`__).


v4.45.0 (2025-12-26)
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10 changes: 7 additions & 3 deletions jsonargparse/_typehints.py
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Expand Up @@ -1063,11 +1063,15 @@ def adapt_typehints(
prev_implicit_defaults = True

if isinstance(prev_val, (dict, Namespace)) and "class_path" not in prev_val:
# implicit prev_val class_path and init_args
prev_val = Namespace(class_path=get_import_path(typehint), init_args=Namespace(prev_val))
# implicit prev_val init_args
prev_val = Namespace(class_path=None, init_args=Namespace(prev_val))

val_input = val
val = subclass_spec_as_namespace(val, prev_val)
if isinstance(prev_val, (dict, Namespace)) and prev_val["class_path"] is None:
type_class_path = Namespace(class_path=get_import_path(typehint))
val = subclass_spec_as_namespace(val, type_class_path)
else:
val = subclass_spec_as_namespace(val, prev_val)
if val and not is_subclass_spec(val) and "init_args" not in val:
# implicit val class_path
val = Namespace(class_path=get_import_path(typehint), init_args=val)
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30 changes: 30 additions & 0 deletions jsonargparse_tests/test_dataclasses.py
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Expand Up @@ -686,6 +686,36 @@ def test_class_path_union_dataclasses(parser):
assert json_or_yaml_load(parser.dump(cfg))["union"] == {"p1": "x", "p2": 0}


@dataclasses.dataclass
class SubA:
a: int = 2


@dataclasses.dataclass
class SubB:
b: float = 3.4


@dataclasses.dataclass
class SubAorB:
a_or_b: Union[SubA, SubB] = dataclasses.field(default_factory=SubA)


def test_union_dataclasses(parser):
parser.add_class_arguments(SubAorB, "data")

cfg = parser.parse_args([])
init = parser.instantiate_classes(cfg)
assert isinstance(init.data, SubAorB)
assert isinstance(init.data.a_or_b, SubA)

cfg = parser.parse_args(["--data.a_or_b.b=4"])
assert cfg.data.a_or_b == Namespace(b=4.0)
init = parser.instantiate_classes(cfg)
assert isinstance(init.data, SubAorB)
assert isinstance(init.data.a_or_b, SubB)


if type_alias_type:
IntOrString = type_alias_type("IntOrString", Union[int, str])

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