example implementation to serialize a given model to xml: https://mail.python.org/pipermail/python-de/2013q4/003488.html

xml-movie-model.py

from lxml import etree
from soapbox import xsd

class Actor(xsd.ComplexType):
    name = xsd.Element(xsd.String)
    role = xsd.Element(xsd.String)

class Actors(xsd.ComplexType):
    actor = xsd.Element(Actor)

class Movie(xsd.ComplexType):
    title = xsd.Element(xsd.String)
    original = xsd.Element(xsd.String, nillable=True)
    url = xsd.Element(xsd.String, nillable=True)
    actors = xsd.Element(Actors)
    runtime = xsd.Element(xsd.Integer)
    aspect_ratio = xsd.Element(xsd.String)

expected_xml = "<movie><title>Ein Hauch von Nerz</title>" \
            + "<original>That Touch of Mink</original>" \
            + "<url>http://de.wikipedia.org/wiki/Ein_Hauch_von_Nerz</url>" \
            + "<actors><actor><name>Sean Connery</name><role>James Bond</role></actor></actors>" \
            + "<runtime>94</runtime>" \
            + "<aspect_ratio>16:9 - 1.77:1</aspect_ratio>" \
            + "</movie>"

actor = Actor()
actor.name = 'Sean Connery'
actor.role = 'James Bond'

actors = Actors()
actors.actor = actor

movie = Movie()
movie.title = "Ein Hauch von Nerz"
movie.original = "That Touch of Mink"
movie.url = "http://de.wikipedia.org/wiki/Ein_Hauch_von_Nerz"
movie.actors = actors
movie.aspect_ratio = "16:9 - 1.77:1"
movie.runtime = 94

document = etree.Element('movie')
movie.render(document, movie)
serialized_xml = etree.tostring(document, pretty_print=True)

assert etree.tostring(etree.fromstring(expected_xml), pretty_print=True) == serialized_xml
print 'generated xml is valid'

parsed = Movie.parsexml(expected_xml)

assert 'Sean Connery' == parsed.actors.actor.name
print 'was able to parse actor name'