[Feature Request] Add exclude_unset and exclude_none options to the to_xml method

[maya-brandi]

Hi! It would be great to have exclude_unset and exclude_none options in the BaseXmlModel.to_xml method. Just as in Pydantics BaseModel.model_dump. I currently have a problem that I dont know how to solve without that option. skip_empty is not enough.

Im including a test to describe the issue.

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "lxml",
#   "pydantic-xml",
# ]
# ///
import unittest
from unittest import TestCase

from lxml import etree
from pydantic_xml import BaseXmlModel, element


VACCINE_XSD = """\
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:simpleType name="LimitedString4Digits">
    <xsd:restriction base="xsd:string">
      <xsd:pattern value="[0-9]{4}"/>
    </xsd:restriction>
  </xsd:simpleType>

  <xsd:complexType name="VaccineType">
    <xsd:sequence>
      <xsd:element name="batchNumber" type="xsd:string" minOccurs="1" maxOccurs="1"/>
      <xsd:element name="municipalityScbCode" type="LimitedString4Digits" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
  </xsd:complexType>
    <xsd:element name="Vaccine" type="VaccineType">
  </xsd:element>
</xsd:schema>
"""
xsd_schema = etree.XMLSchema(etree.fromstring(VACCINE_XSD))


class VaccineType(
    BaseXmlModel,
    nsmap={"xsi": "http://www.w3.org/2001/XMLSchema-instance"},
    tag="Vaccine",
):
    batch_number: str = element(tag="batchNumber")
    municipality_scb_code: str | None = element(
        tag="municipalityScbCode", default=None, pattern="[0-9]{4}"
    )


class TestSkipEmpty(TestCase):
    """
    Test the same document validated against the same XSD,
    with different settings for `skip_empty`.
    
    These two tests will fail in different ways.
    """
    def test_skip_empty_true(self) -> None:
        vaccine = VaccineType(batch_number="")
        # When `skip_empty = True`, `batchNumber` is skipped when empty,
        # but it is mandatory.
        vaccine_xml = vaccine.to_xml(skip_empty=True)
        xsd_schema.assertValid(etree.fromstring(vaccine_xml))

    def test_skip_empty_false(self) -> None:
        vaccine = VaccineType(batch_number="")
        # When `skip_empty = False`, `municipalityScbCode` is included,
        # but it's not allowed when empty.
        vaccine_xml = vaccine.to_xml(skip_empty=False)
        xsd_schema.assertValid(etree.fromstring(vaccine_xml))


if __name__ == "__main__":
    unittest.main()

[dapper91]

@maya-brandi Hi

Implemented this feature in version 2.12.0.

[maya-brandi]

Fantastic! Thanks!