How to work with wildcard fields?

One of the xml schema traits is to support any extensions with wildcards.

<xs:complexType name="MetadataType" mixed="false">
    <xs:sequence>
        <xs:any namespace="##any" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

The generator will roughly create this class for you.

>>> from dataclasses import dataclass
>>> from dataclasses import field
>>> from typing import Dict
>>> from typing import List
...
>>> @dataclass
... class MetadataType:
...     any_element: List[object] = field(
...         default_factory=list,
...         metadata={
...              "type": "Wildcard",
...              "namespace": "##any",
...          }
...     )
...     other_attributes: Dict[str, str] = field(
...          default_factory=dict,
...          metadata={
...              "type": "Attributes",
...              "namespace": "##other",
...          }
...      )

xsdata comes with two generic models that are used during parsing and you can also use to generate any custom xml element.

Model	Description
AnyElement	Used to represent any xml structure, resembles a DOM Element
DerivedElement	Wrapper for type substitution elements eg <b xsi:type=”a”>…</b>

>>> from xsdata.formats.dataclass.models.generics import AnyElement
>>> from xsdata.formats.dataclass.models.generics import DerivedElement
>>> from xsdata.formats.dataclass.serializers import XmlSerializer
>>> from xsdata.formats.dataclass.serializers.config import SerializerConfig
...
>>> obj = MetadataType(
...     any_element=[
...         AnyElement(
...             qname="bar",
...             children=[
...                 AnyElement(qname="first", text="1st", attributes={"a": "1"}),
...                 AnyElement(qname="second", text="2nd", attributes={"b": "2"}),
...                 DerivedElement(
...                     qname="third",
...                     value=MetadataType(other_attributes={"c": "3"})
...                 )
...             ]
...         )
...     ]
... )
>>> config = SerializerConfig(pretty_print=True, xml_declaration=False)
>>> serializer = XmlSerializer(config=config)
>>> print(serializer.render(obj))
<MetadataType>
  <bar>
    <first a="1">1st</first>
    <second b="2">2nd</second>
    <third xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" c="3" xsi:type="MetadataType"/>
  </bar>
</MetadataType>