Question

I am generating an SVG file that’s intended to include Inkscape-specific tags. For example, inkscape:label and inkscape:groupmode. I am using lxml etree as my parser/generator. I’d like to add the label and groupmode tags to the following instance:

layer = etree.SubElement(svg_instance, 'g', id="layer-id")

My question is how do I achieve that in order to get the correct output form in the SVG, for example:

<g inkscape:groupmode="layer" id="layer-id" inkscape:label="layer-label">

Answer 1

First, remember that inkscape: isnt’ a namespace, it’s just a convenient way of referring to a namespace that is defined in your XML root element. The namespace is http://www.inkscape.org/namespaces/inkscape, and depending on your XML, inkscape:groupmode might be identical to foo:groupmode. And of course, your <g> element is part of the SVG namespace, http://www.w3.org/2000/svg. To generate appropriate output with LXML, you would start with something like this:

from lxml import etree
root = etree.Element('{http://www.w3.org/2000/svg}svg')
g = etree.SubElement(root, '{http://www.w3.org/2000/svg}g', id='layer-id')

Which would get you:

<ns0:svg xmlns:ns0="http://www.w3.org/2000/svg">
  <ns0:g id="layer-id"/>
</ns0:svg>

To add in the inkscape-specific attributes, you would do this:

g.set('{http://www.inkscape.org/namespaces/inkscape}groupmode', 'layer')
g.set('{http://www.inkscape.org/namespaces/inkscape}label', 'layer-label')

Which would get you:

<ns0:svg xmlns:ns0="http://www.w3.org/2000/svg">
  <ns0:g xmlns:ns1="http://www.inkscape.org/namespaces/inkscape" id="layer-id" ns1:groupmode="layer" ns1:label="layer-label"/>
</ns0:svg>

Which believe it or not is exactly what you want. You can clean up the namespace labels a bit by passing an nsmap= parameter when creating your root element. Like this:

NSMAP = {
  None: 'http://www.w3.org/2000/svg',
'inkscape': 'http://www.inkscape.org/namespaces/inkscape',
}

root = etree.Element('{http://www.w3.org/2000/svg}svg', nsmap=NSMAP)

With this in place, the final output would look like this:

<svg xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape" xmlns="http://www.w3.org/2000/svg">
  <g id="layer-id" inkscape:label="layer-label" inkscape:groupmode="layer"/>
</svg>

More information in the LXML documentation.