output

<Foo>
  <node_b>more_data</node_b>
  <node_a ATTR="1st">data1</node_a>
  <node_a ATTR="2nd">data2</node_a>
</Foo>

xmldata_example.py

from spyne import *
from spyne.util.xml import get_object_as_xml
from lxml import etree

class Node(ComplexModel):
    ATTR = XmlAttribute(Unicode)
    data = XmlData(Unicode(max_len=450, values=['1st', '2nd']))


class Foo(ComplexModel):
    node_a = Node.customize(max_occurs=2)
    node_b = Unicode(max_len=450)

elt = get_object_as_xml(
  Foo(
    node_a=[
      Node('data1', ATTR='1st'),
      Node('data2', ATTR='2nd'),
    ],
    node_b="more_data",
  ), 
  Foo
)

print(etree.tostring(elt, pretty_print=True))