How to add an attribute to a tag found using xpath in lxml in Python?

Question

I have the following xml -

<draw:image></draw:image>

I want to add multiple xlink attributes to it and make it -

<draw:image xlink:href="image" xlink:show="embed"></draw:image>

I tried using the following code but got the error "ValueError: Invalid attribute name u'xlink:href'"

root.xpath("//draw:image", namespaces=
{"draw":"urn:oasis:names:tc:opendocument:xmlns:drawing:1.0"})
[0].attrib['xlink:href'] = 'image'

What am I doing wrong? There seems to be something related to namespaces, but I can't figure what.

Can you add a link to the actual file? Or at least a stripped down usable version with the namespace decs etc,.. — Padraic Cunningham
– Padraic Cunningham, Commented Jun 9, 2016 at 0:06
@PadraicCunningham Ah. Okay. Here are the namespaces - gist.github.com/shrox/df592e65a8848dd4f0ddab18cc340dd4 — Shreedhar Manek
– Shreedhar Manek, Commented Jun 9, 2016 at 0:14
Can you add a watered down version of the file? It will be easier to just show you a complete example. — Padraic Cunningham
– Padraic Cunningham, Commented Jun 9, 2016 at 0:28
@PadraicCunningham I did! The namespaces with the tag in question. gist.github.com/shrox/df592e65a8848dd4f0ddab18cc340dd4 — Shreedhar Manek
– Shreedhar Manek, Commented Jun 9, 2016 at 0:30
I just need to know how to make .attrib work with attributes with a prefix. — Shreedhar Manek
– Shreedhar Manek, Commented Jun 9, 2016 at 0:31

Padraic Cunningham · Accepted Answer · 2016-06-09 01:09:39Z

This is a working example:

from lxml import etree as et

xml = et.parse("your.xml")
root = xml.getroot()
d = root.nsmap

for node in root.xpath("//draw:image", namespaces=d):
    node.attrib["{http://www.w3.org/1999/xlink}href"] = "value"
    node.attrib["{http://www.w3.org/1999/xlink}show"] = "embed"
print(et.tostring(xml))

Which for:

<?xml version="1.0" encoding="utf-8"?>
<office:document xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0"
xmlns:style="urn:oasis:names:tc:opendocument:xmlns:style:1.0"
xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0"
xmlns:table="urn:oasis:names:tc:opendocument:xmlns:table:1.0"
xmlns:draw="urn:oasis:names:tc:opendocument:xmlns:drawing:1.0"
xmlns:fo="urn:oasis:names:tc:opendocument:xmlns:xsl-fo-compatible:1.0"
xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns:meta="urn:oasis:names:tc:opendocument:xmlns:meta:1.0"
xmlns:number="urn:oasis:names:tc:opendocument:xmlns:datastyle:1.0"
xmlns:svg="urn:oasis:names:tc:opendocument:xmlns:svg-compatible:1.0"
xmlns:chart="urn:oasis:names:tc:opendocument:xmlns:chart:1.0"
xmlns:dr3d="urn:oasis:names:tc:opendocument:xmlns:dr3d:1.0">
<draw:image></draw:image>

Outputs:

<office:document xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0" xmlns:style="urn:oasis:names:tc:opendocument:xmlns:style:1.0" xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0" xmlns:table="urn:oasis:names:tc:opendocument:xmlns:table:1.0" xmlns:draw="urn:oasis:names:tc:opendocument:xmlns:drawing:1.0" xmlns:fo="urn:oasis:names:tc:opendocument:xmlns:xsl-fo-compatible:1.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:meta="urn:oasis:names:tc:opendocument:xmlns:meta:1.0" xmlns:number="urn:oasis:names:tc:opendocument:xmlns:datastyle:1.0" xmlns:svg="urn:oasis:names:tc:opendocument:xmlns:svg-compatible:1.0" xmlns:chart="urn:oasis:names:tc:opendocument:xmlns:chart:1.0" xmlns:dr3d="urn:oasis:names:tc:opendocument:xmlns:dr3d:1.0">
<draw:image xlink:href="value" xlink:show="embed"/>


</office:document>

Or using set:

for node in root.xpath("//draw:image", namespaces=d):
    node.set("{http://www.w3.org/1999/xlink}href", "image")
    node.set("{http://www.w3.org/1999/xlink}show", "embed")

You have no idea how helpful you've been. I've been having difficulty in understanding how namespaces work since yesterday and this has simplified it for me. Thank you!

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