How to customize namespace prefix in objects inheriting from lxml.ElementBase

Question

From the lxml documentation, I understand that custom XML elements should inherit from ElementBase.

For instance, I can create

class FactVariable(etree.ElementBase):
    ''' Class that represents a XBRL fact variable.'''
    TAG = '{http://xbrl.org/2008/variable}factVariable'

    @property
    def label(self):
        return self.attrib['{http://www.w3.org/1999/xlink}label']

    @label.setter
    def label(self, value):
        self.attrib['{http://www.w3.org/1999/xlink}label'] = value

My problem is that when I create a XML tree and place such nodes, I get

<ns0:factVariable xmlns:ns0="http://xbrl.org/2008/variable" label="azerty"/>

Question: I want the namespace to be prefixed va, not ns0 How can I change that?

I tried to set the self.nsmap property, but I have a "read-only" exception. Adding a key/value has no effect (as said in the documentation).

I also tried, without success

etree.register_namespace('va', 'http://xbrl.org/2008/variable')

lorenzosu · Accepted Answer · 2012-07-13 12:14:39Z

3

I know this is old and probably @rds solved this, but I was encountering a similar problem, so thought I'd share som info. It seems that setting the nsmap upon creation will at least work:

>>> etree.tostring(FactVariable(label='qwerty', nsmap={'va':'http://xbrl.org/2008/variable'}))
'<va:factVariable xmlns:va="http://xbrl.org/2008/variable" label="qwerty"/>'

answered Jul 13, 2012 at 12:14

lorenzosu

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