Python 3.10 pipe Union type hints not supported

[jwfraustro]

Currently, the Model1 | Model2 Python 3.10 syntax of a union is not recognized between models by pydantic-xml.

This can be replicated pretty easily by changing the TestModel class here to use them:

pydantic-xml/tests/test_unions.py

Lines 32 to 40 in 68ce048

	def test_model_union():
	class SubModel1(BaseXmlModel, tag='model1'):
	attr1: int = attr()
	class SubModel2(BaseXmlModel, tag='model2'):
	text: float
	class TestModel(BaseXmlModel, tag='model'):
	field1: Union[SubModel1, SubModel2] = element()

as in:

    class TestModel(BaseXmlModel, tag='model'):
        field1: SubModel1 | SubModel2 = element()

this will fail when .from_xml() is called (and in testing my project, when to_xml() is called also) with

>   ???
E   pydantic.error_wrappers.ValidationError: 1 validation error for TestModel
E   field1
E     field required (type=value_error.missing)

pydantic/main.py:341: ValidationError

The cause for this is this function:

pydantic-xml/pydantic_xml/serializers/serializer.py

Lines 69 to 70 in 68ce048

	def is_union(type_: Any) -> bool:
	return typing.get_origin(type_) is Union

Unions denoted by the | in Python 3.10 are actually types.UnionType rather than typing.Union.


typing.get_origin() actually returns it specifically:



https://github.com/python/cpython/blob/a5d2b546c1b0b73d0695b98838a3ddd497382999/Lib/typing.py#L2412-L2413



The fix is just adding UnionType to the is_union() function.