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How to add attribute to tag found with xpath in lxml in Python?

I have the following xml -

<draw:image></draw:image>

I want to add some xlink attributes to it and do this -

<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? Something seems to be related to namespaces, but I can't figure that out.

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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))

What 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")
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