python xml pretty print not working

Question

I am changing an some xml by adding some nodes and values from a list. I can successfully create all the new tags and values, I am creating them between the contributors tags, but when I save the xml out to a new file, the tags I create are all on one line. Here is a sample of my code:

templateXml = """<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<package>
  <delivery_type>new</delivery_type>
  <feature>
    <feature_type>Movie</feature_type>
    <contributors>
    </contributors>
</package>"""

from lxml import etree
tree = etree.fromstring(templateXml)

node_video = tree.xpath('//feature/contributors')[0]
for cast in castList:
    pageElement = etree.SubElement(node_video, 'contributor')
    node_video1 = tree.xpath('//feature/contributors/contributor')[0]
    pageElement.attrib['type'] = 'cast'
    pageElement1 = etree.SubElement(pageElement, 'name')
    pageElement1.text = cast.text
    pageElement2 = etree.SubElement(pageElement, 'role')
    pageElement2.text = "actor"

xmlFileOut = '/Users/User1/Desktop/Python/Done.xml'   

with open(xmlFileOut, "w") as f:
    f.write(etree.tostring(tree, pretty_print = True, xml_declaration = True, encoding='UTF-8', standalone="yes"))

Here is saved xml file:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<package>
  <delivery_type>new</delivery_type>
  <feature>
    <feature_type>Movie</feature_type>
    <contributors>
    <contributor type="cast"><name>John Doe</name><role>actor</role></contributor><contributor type="cast"><name>Another Actors name</name><role>actor</role></contributor><contributor type="cast"><name>Jane Doe</name><role>actor</role></contributor><contributor type="cast"><name>John Smith</name><role>actor</role></contributor></contributors>
</package>

I have solved this issue when opening an xml file to work on using the below code:

from lxml import etree
parser = etree.XMLParser(remove_blank_text=True) # makes pretty print work
path3 = 'path_to_xml_file'
open(path3)
tree = etree.parse(path3, parser)
root = tree.getroot()
tree.write(xmlFileOut, pretty_print = True, xml_declaration = True, encoding = 'UTF-8')

This works, but how do I get it to work with a string xml?

Answer 1

Taken from http://ruslanspivak.com/2014/05/12/how-to-pretty-print-xml-with-lxml/

import StringIO
import lxml.etree as etree

def prettify(xml_text):
    """Pretty prints xml."""
    parser = etree.XMLParser(remove_blank_text=True)
    file_obj = StringIO.StringIO(xml_text)
    tree = etree.parse(file_obj, parser)
    return etree.tostring(tree, pretty_print=True)