Python 2.7 and xml.etree: how to create an XML file with multiple namespaces?

Question

I'm trying to create an XML file so that it has the following skeleton, preferably using the xml.etree modules in Python 2.7:

<?xml version="1.0"?>
<foo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" thing1="this" thing2="that">
  ....
  <somedata bar="1">
    <moredata whatsit="42"></moredata>
  </somedata>
  ....
</foo>

It's the "foo ...." line that vexes me. I tried using nsmap for bringing in xsi and xsd, but that led to a "cannot serialize" error.

I could construct or otherwise hack that line's text to be exactly as I want it, but I'd like to learn to do this programmatically using xml.etree (pulling in an external library is not preferable in this situation).

I'd think this is a common pattern but I'm just not finding it anywhere for Python and etree.

Answer 1

If the prefixes are used in the document; you could call register_namespace() to add them:

import sys
import xml.etree.ElementTree as etree

xsi =  "http://www.w3.org/2001/XMLSchema-instance"
xsd =  "http://www.w3.org/2001/XMLSchema"
ns = {"xmlns:xsi": xsi, "xmlns:xsd": xsd}
for attr, uri in ns.items():
    etree.register_namespace(attr.split(":")[1], uri)

foo = etree.Element("foo",
    dict(thing1="this", thing2="that")) # put `**ns))` if xsi, xsd are unused
somedata = etree.SubElement(foo, "somedata", dict(bar="1"))
etree.SubElement(somedata, "moredata",
    {"whatsit": "42", etree.QName(xsi, "type"): etree.QName(xsd, "string")})

etree.ElementTree(foo).write(sys.stdout, xml_declaration=True)

Otherwise, you could set the attributes explicitly (ns dict) if you need it.

Answer 2

import xml.etree.ElementTree as et

foo = et.Element('foo', **{'xmlns:xsi': 'http://www.w3.org/2001/XMLSchema-instance'}, **{'xmlns:xsd': 'http://www.w3.org/2001/XMLSchema'})
somedata = et.SubElement(foo, 'somedata', bar='1')
moredata = et.SubElement(somedata, 'moredata', whatsit='42')
tree = et.ElementTree(foo)
tree.write('file.xml')