Sample pre_load and xml in marshmallow

marshmallow_xml.py

from xml.etree.ElementTree import Element
import xml.etree.ElementTree as ET

from marshmallow import (Schema, pre_load)

from marshmallow.fields import (
    Str,
    Integer,
    List,
    Nested
)
from marshmallow.exceptions import ValidationError

class BaseSchema(Schema):

    @staticmethod
    def _extract_value(k, v, elt):
        try:
            if isinstance(v, Nested):
                return v.schema.__class__().load(elt)
            else:
                return elt.text
        except AttributeError as e:
            print(f'key {k} unknown')
            return ''

    @pre_load
    def _(self, data, many, **kwargs):
        if isinstance(data, Element):
            res = dict()
            for k, v in self.declared_fields.items():
                try:
                    if isinstance(v, Nested) and v.many:
                        res[k] = [self._extract_value(k, v, elt) for elt in data.findall(k)]
                    else:
                        elt = data.find(k)
                        res[k] = self._extract_value(k, v, elt)
                except ValidationError as e:
                    print(f'key {k} unknown')
                    res[k] = {}
            return res
        return data

class A(BaseSchema):
    name = Str()
    slug = Str()
    qsdq = Str()

class B(BaseSchema):
    aze = Integer()
    xcw = Nested(A(), many=True)
    qsd = Nested(A(), many=True)
   # df = Nested(A())


class root(BaseSchema):
    B = Nested(B())

xml = ET.fromstring('''<root><B><aze>1</aze><qsd><name>NAME</name><slug>SLUG</slug></qsd>
                    <qsd><name>NAME1</name><slug>SLUG2</slug></qsd></B></root>''')

root().load(xml)