XML Declaration standalone="yes" lxml

Question

I have an xml I am parsing, making some changes and saving out to a new file. It has the declaration <?xml version="1.0" encoding="utf-8" standalone="yes"?> which I would like to keep. When I am saving out my new file I am loosing the standalone="yes" bit. How can I keep it in? Here is my code:

templateXml = """<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<package>
  <provider>Some Data</provider>
  <studio_display_name>Some Other Data</studio_display_name>
</package>"""

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

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'))

Answer 1

You can pass standalone keyword argument to tostring():

etree.tostring(tree, pretty_print = True, xml_declaration = True, encoding='UTF-8', standalone=True)

Answer 2

Specify standalone using tree.docinfo.standalone.

Try following:

from lxml import etree
tree = etree.fromstring(templateXml).getroottree() # NOTE: .getroottree()

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=tree.docinfo.encoding,
                           standalone=tree.docinfo.standalone))