Parsing a complicated XML file with Python

Question

I am trying to parse a very ugly XML file with Python. I manage to get pretty well into it, but at the npdoc element it fails. What am I doing wrong?

XML:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<npexchange xmlns="http://www.example.com/npexchange/3.5" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="3.5">
<article id="123" refType="Article">
<articleparts>
    <articlepart id="1234" refType="ArticlePart">
        <data>
            <npdoc xmlns="http://www.example.com/npdoc/2.1" version="2.1" xml:lang="sv_SE">
                <body>
                    <p>Lorem ipsum some random text here.</p>
                    <p>
                        <b>Yes this is HTML markup, and I would like to keep that.</b>
                    </p>
                </body>
                <headline>
                    <p>I am a headline</p>
                </headline>
                <leadin>
                    <p>I am some other text</p>
                </leadin>
            </npdoc>
        </data>
    </articlepart>
</articleparts>
</article>
</npexchange>

This is the python code I have so far:

from xml.etree.ElementTree import ElementTree

def parse(self):
    tree = ElementTree(file=filename)

    for item in tree.iter("article"):
        articleParts = item.find("articleparts")
        for articlepart in articleParts.iter("articlepart"):
            data = articlepart.find("data")
            npdoc = data.find("npdoc")

            id = item.get("id")
            headline = npdoc.find("headline").text
            leadIn = npdoc.find("leadin").text
            body = npdoc.find("body").text


    return articles

What happens is that I get the id out, but the fields that are inside the npdoc element I cannot access. The npdoc variable gets set to None.

Update: Managed to get the elements into variables by using the namespace in the .find() calls. How do I get the value? As it is HTML it does not come out correctly with the .text attribute.

That is not a valid XML document. It does not have a root elment. — user1907906
– user1907906, Commented Apr 20, 2015 at 9:11
The expected outcome is that the string <p>I am a headline</p> in the headline variable, and so on. — Tebro
– Tebro, Commented Apr 20, 2015 at 9:12
There is a root element, going to edit it in now. My cleaning was a little aggressive. — Tebro
– Tebro, Commented Apr 20, 2015 at 9:14
THis is a namespace problem. Is it possible to define a prefix like xmlns:n for the http://www.example.com/npdoc/2.1 namespace? Without such a prefix it is difficult to access the elements under this namespace. — user1907906
– user1907906, Commented Apr 20, 2015 at 9:53

Charles Duffy · Accepted Answer · 2015-04-20 14:04:23Z

2

nsmap = {'npdoc': 'http://www.example.com/npdoc/2.1'}
data = articlepart.find("npdoc:data", namespaces=nsmap)

...will find your data element. No ugly, unreliable string munging required. (Re: "unreliable" -- consider what this would do to CDATA sections containing literal arrow brackets).

edited Apr 20, 2015 at 14:04

answered Apr 20, 2015 at 13:58

Charles Duffy

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Comments

Gord Thompson · Accepted Answer · 2016-05-13 17:16:55Z

1

This is what I came up with in Python 3.4. It's certainly not bulletproof, but it might give you some ideas.

import xml.etree.ElementTree as ET
tree = ET.parse(r'C:\Users\Gord\Desktop\nasty.xml')
npexchange = tree.getroot()
for article in npexchange:
    for articleparts in article:
        for articlepart in articleparts:
            id = articlepart.attrib['id']
            print("ArticlePart - id: {0}".format(id))
            for data in articlepart:
                for npdoc in data:
                    for child in npdoc:
                        tag = child.tag[child.tag.find('}')+1:]
                        print("    {0}:".format(tag))  ## e.g., "body:"
                        contents = ET.tostring(child).decode('utf-8')
                        contents = contents.replace('<ns0:', '<')
                        contents = contents.replace('</ns0:', '</')
                        contents = contents.replace(' xmlns:ns0="http://www.example.com/npdoc/2.1">', '>')
                        contents = contents.replace('<' + tag + '>\n', '')
                        contents = contents.replace('</' + tag + '>', '')
                        contents = contents.strip()
                        print("        {0}".format(contents))

The console output is

ArticlePart - id: 1234
    body:
        <p>Lorem ipsum some random text here.</p>
                            <p>
                                <b>Yes this is HTML markup, and I would like to keep that.</b>
                            </p>
    headline:
        <p>I am a headline</p>
    leadin:
        <p>I am some other text</p>

Update

Somewhat improved version with

a Namespace map (as suggested by Charles),
register_namespace with an empty prefix to remove some namespace prefix "noise", and
using .findall() instead of blindly iterating through child nodes regardless of their tag:

import xml.etree.ElementTree as ET
npdoc_uri = 'http://www.example.com/npdoc/2.1'
nsmap = {
    'npexchange': 'http://www.example.com/npexchange/3.5',
    'npdoc': npdoc_uri
    }
ET.register_namespace("", npdoc_uri)
tree = ET.parse(r'/home/gord/Desktop/nasty.xml')
npexchange = tree.getroot()
for article in npexchange.findall('npexchange:article', nsmap):
    for articleparts in article.findall('npexchange:articleparts', nsmap):
        for articlepart in articleparts.findall('npexchange:articlepart', nsmap):
            id = articlepart.attrib['id']
            print("ArticlePart - id: {0}".format(id))
            for data in articlepart.findall('npexchange:data', nsmap):
                for npdoc in data.findall('npdoc:npdoc', nsmap):
                    for child in npdoc.getchildren():
                        tag = child.tag[child.tag.find('}')+1:]
                        print("    {0}:".format(tag))  ## e.g., "body:"
                        contents = ET.tostring(child).decode('utf-8')
                        # remove HTML block tags, e.g. <body ...> and </body>
                        contents = contents.replace('<' + tag + ' xmlns="' + npdoc_uri + '">\n', '')
                        contents = contents.replace('</' + tag + '>', '')
                        contents = contents.strip()
                        print("        {0}".format(contents))

edited May 13, 2016 at 17:16

answered Apr 20, 2015 at 12:55

Gord Thompson

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7 Comments

Tebro Over a year ago

This looks promising, had to do some modifications as there is more stuff than just <article> elements in the root. (and a lot more crap in the <article> element) but I have something working at the moment.

Gord Thompson Over a year ago

I had a hunch that there may have been more elements. I considered adding an if thing.tag == 'thing': block inside each loop but I thought it might clutter things up too much.

Tebro Over a year ago

One thing that it seems to do though is that it removes closing tags (</p> and such)

Gord Thompson Over a year ago

Aha. contents.replace('</ns0:', '<') changed to contents.replace('</ns0:', '</')..

Charles Duffy Over a year ago

WTF? Why in the world would you round-trip through text and use string replacements rather than just changing the namespace map?

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