How to insert namespace and prefixes into an XML string with Python?

I don't think this can be done with just ElementTree.

Manipulating namespaces is sometimes surprisingly tricky. There are many questions about it here on SO. Even with the more advanced lxml library, it can be really hard. See these related questions:

• lxml: add namespace to input file
• Modify namespaces in a given xml document with lxml
• lxml etree xmlparser remove unwanted namespace

Below is a solution that uses XSLT.

Code:

from lxml import etree

XML = '''
<A>
    <B foo="123">
        <C>thing</C>
        <D>stuff</D>
    </B>
</A>'''

XSLT = '''
<xsl:stylesheet version="1.0"
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:ns1="www.example.com">
 <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>

  <xsl:template match="*">
   <xsl:element name="ns1:{name()}">
    <xsl:apply-templates select="node()|@*"/>
   </xsl:element>
  </xsl:template>

  <!-- No prefix on the A element -->
  <xsl:template match="A">
   <A xmlns:ns1="www.example.com">
    <xsl:apply-templates select="node()|@*"/>
   </A>
  </xsl:template>
</xsl:stylesheet>'''

xml_doc = etree.fromstring(XML)
xslt_doc = etree.fromstring(XSLT)
transform = etree.XSLT(xslt_doc)
print transform(xml_doc)

Output:

<A xmlns:ns1="www.example.com">
    <ns1:B foo="123">
        <ns1:C>thing</ns1:C>
        <ns1:D>stuff</ns1:D>
    </ns1:B>
</A>

Use ET.register_namespace('ns1', 'www.example.com') to register the namespace with ElementTree. This is needed so write() uses the registered prefix. (I have code that uses a prefix of '' (an empty string) for the default namespace)

Then prefix each element name with {www.example.com}. For example: root.find('{www.example.com}B').

import xml.etree.ElementTree as ET

name_space = {
# namespace defined below
"xmlns:ns1":"www.example.com""="www.example.com"
}

A = ET.Element('A', name_space)
B = ET.SubElement(A, 'ns1:B')
C = ET.SubElement(B, 'ns1:C')
C.text = 'thing'

You can pass the namespaces to the Element constructor, at that point you can reference if at any child component. note you can define more than one. this solution worked for me.