Python: specify XMLNS on xml.etree elements

Question

in my Python code I'm currently using the xml.etree library to create a tree and then dump it to an XML string. Unfortunately I can't use modules other than the ones in the Python Standard Libraries to do that.

Here is my code:

import xml.etree.ElementTree as ET

def dump_to_XML():
  root_node = ET.Element("root")
  c1_node = ET.SubElement(root_node, "child1")
  c1_node.text = "foo"
  c2_node = ET.SubElement(root_node, "child2")
  gc1_node = ET.SubElement(c2_node, "grandchild1")
  gc1_node.text = "bar"
  return ET.tostring(root_node, encoding='utf8', method='xml')

which gives the string:

<?xml version='1.0' encoding='utf8'?>
<root>
    <child1>foo</child1>
    <child2>
        <grandchild1>bar</grandchild1>
    </child2>
</root>

Now, I have two schema files located - say - http://myhost.com/p.xsd and http://myhost.com/q.xsd, I want the output string to be turned into:

<?xml version='1.0' encoding='UTF-8'?>
<root xmlns:p="http://myhost.com/p.xsd" xmlns:q="http://myhost.com/q.xsd">
    <p:child1>foo</p:child1>
    <p:child2>
        <q:grandchild1>bar</q:grandchild1>
    </p:child2>
</root>

How can I leverage the etree library in order to achieve that?

Thanks in advance