Parse XML where an element prefix is defined in the same element

Question

I have an XML file with an element which looks like this:

<wrapping_element>
    <prefix:tag xmlns:prefix="url">value</prefix:tag>
</wrapping_element>

I want to get this element, so I am using lxml as follows:

wrapping_element.find('prefix:tag', wrapping_element.nsmap)

but I get the following error: SyntaxError: prefix 'prefix' not found in prefix map because prefix is not defined before reaching this element in the XML.

Is there a way to get the element anyway?

I think the problem is rather that wrapping_element.nsmap is empty. I don't even find find in the documentation labyrinth, but there seems to be a method xpath too, maybe you can use it. — Arndt Jonasson
– Arndt Jonasson, Commented May 17, 2018 at 9:24
@ArndtJonasson The thing is, xpath requires a namespaces argument as find does. My problem is that I can't find a way to retrieve the namespace without the element nor the element without the namespace. — mckbrd
– mckbrd, Commented May 17, 2018 at 9:49
How about wrapping_element.xpath('/*/*[local-name()="tag"]')? — Arndt Jonasson
– Arndt Jonasson, Commented May 17, 2018 at 11:51
@ArndtJonasson Great! I used a relative path: wrapping_element.xpath('./*[local-name()="tag"]'), it's working perfectly. Thanks a lot! — mckbrd
– mckbrd, Commented May 17, 2018 at 12:06

Daniel Haley · Accepted Answer · 2018-05-17 17:37:21Z

1

Like mentioned in the comments, you could use local-name() to circumvent the namespace, but it's easy enough to just handle the namespace directly in the xpath() call...

from lxml import etree

tree = etree.parse("input.xml")

wrapping_element = tree.xpath("/wrapping_element")[0]
tag = wrapping_element.xpath("x:tag", namespaces={"x": "url"})[0]

print(etree.tostring(tag, encoding="unicode"))

This will print...

<prefix:tag xmlns:prefix="url">value</prefix:tag>

Notice I used the prefix x. The prefix can match the prefix in the XML file, but it doesn't have to; only the namespace URIs need to match exactly.

See here for more details: http://lxml.de/xpathxslt.html#namespaces-and-prefixes

answered May 17, 2018 at 17:37

Daniel Haley

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