How to generate XML documents with namespaces in Python

Question

I'm trying to generate an XML document with namespaces, currently with Python's xml.dom.minidom:

import xml.dom.minidom
doc = xml.dom.minidom.Document()
el = doc.createElementNS('http://example.net/ns', 'el')
doc.appendChild(el)
print(doc.toprettyxml())

The namespace is saved (doc.childNodes[0].namespaceURI is 'http://example.net/ns'), but why is it missing in the output?

<?xml version="1.0" ?>
<el/>

I expect:

<?xml version="1.0" ?>
<el xmlns="http://example.net/ns" />

or

<?xml version="1.0" ?>
<randomid:el xmlns:randomid="http://example.net/ns" />

Answer 1

createElementNS() is defined as:

def createElementNS(self, namespaceURI, qualifiedName):
    prefix, localName = _nssplit(qualifiedName)
    e = Element(qualifiedName, namespaceURI, prefix)
    e.ownerDocument = self
    return e

so...

import xml.dom.minidom
doc = xml.dom.minidom.Document()
el = doc.createElementNS('http://example.net/ns', 'ex:el')
#--------------------------------------------------^^^^^
doc.appendChild(el)
print(doc.toprettyxml())

yields:

<?xml version="1.0" ?>
<ex:el/>

...not quite there...

import xml.dom.minidom
doc = xml.dom.minidom.Document()
el = doc.createElementNS('http://example.net/ns', 'ex:el')
el.setAttribute("xmlns:ex", "http://example.net/ns")
doc.appendChild(el)
print(doc.toprettyxml())

yields:

<?xml version="1.0" ?>
<ex:el xmlns:ex="http://example.net/ns"/&gt;

alternatively:

import xml.dom.minidom
doc = xml.dom.minidom.Document()
el = doc.createElementNS('http://example.net/ns', 'el')
el.setAttribute("xmlns", "http://example.net/ns")
doc.appendChild(el)
print(doc.toprettyxml())

wich produces:

<?xml version="1.0" ?>
<el xmlns="http://example.net/ns"/&gt;

It looks like you'd have to do it manually. Element.writexml() shows no indication that namespaces would get any special treatment.

EDIT: This answer is targeted at xml.dom.minidom only, since the OP used it in the question. I do not indicate that it was impossible to use XML namespaces in Python generally. ;-)

Answer 2

This feature is already proposed; a patch is slumbering in the Python bug database. See Tomalak's answer (in short: Manually add the xmlns attribute) for a workaround.