How to remove elements from XML using Python

Question

Hi, I got stuck with XML and Python. The task is simple but I couldn't resolve it so far and spent on that long time. I came here for an advice how to solve it with couple of lines.

Thanks for any help with traversing the tree. I always ended up with too many or too few elements. Elements can be nested without limit. Given example is just an example. I will accept any solution, not picky about dom, minidom, sax, whatever..

I have an XML file similar to this one:

<root>
    <elm>
        <elm>Common content</elm>

        <elm xmlns="http://example.org/ns"&gt;
            <elm lang="en">Content EN</elm>
            <elm lang="cs">žluťoučký koníček</elm>
        </elm>

        <elm xml:id="abc123">Common content</elm>

        <elm lang="en">Content EN</elm>
        <elm lang="cs">Content CS</elm>

        <elm lang="en">
            <elm>Content EN</elm>
            <elm>Content EN</elm>
        </elm>

        <elm lang="cs">
            <elm>Content CS</elm>
            <elm>Content CS</elm>
        </elm>
    </elm>
</root>

What I need - parse the XML and write a new file. The new file should contain all the elements for given language and elements without lang attribute.

For "cs" language the output file should containt this:

<root>
    <elm>
        <elm>Common content</elm>

        <elm xmlns="http://example.org/ns"&gt;
            <elm lang="cs">žluťoučký koníček</elm>
        </elm>

        <elm xml:id="abc123">Common content</elm>

        <elm lang="cs">Content CS</elm>

        <elm lang="cs">
            <elm>Content CS</elm>
            <elm>Content CS</elm>
        </elm>
    </elm>
</root>

If you can make it to omit the lang attribute in the new file, even better. But it's not that important.

UPDATE1: Added unicode characters and namespace attribute.

UPDATE2: Using Python 2.5, standard libraries preferred.

Answer 1

I'm not sure how best to remove the lang attribute, but here's some code that does the other changes (Python 2.7; for 2.5 or 2.6, use getIterator instead of iter), assuming that when you remove an element you also always want to remove everything contained in that element.

This code just prints the result to standard output (you could redirect it as you wish, of course, or directly write it to some new file, and so on):

import sys
from xml.etree import cElementTree as et

def picklang(path, lang='en'):
    tr = et.parse(path)
    for element in tr.iter():
        for subelement in element:
            la = subelement.get('lang')
            if la is not None and la != lang:
                element.remove(subelement)
    return tr

if __name__ == '__main__':
    tr = picklang('la.xml')
    tr.write(sys.stdout)
    print

With la.xml being your example, this writes

<root>
    <elm>Common content</elm>

    <elm>
        <elm lang="en">Content EN</elm>
        </elm>

    <elm>Common content</elm>

    <elm lang="en">Content EN</elm>
    <elm lang="en">
        <elm>Content EN</elm>
        <elm>Content EN</elm>
    </elm>

    </root>

Answer 2

Using lxml:

import lxml.etree as le

with open('doc.xml','r') as f:
    doc=le.parse(f)
    for elem in doc.xpath('//*[attribute::lang]'):
        if elem.attrib['lang']=='en':
            elem.attrib.pop('lang')
        else:
            parent=elem.getparent()
            parent.remove(elem)
    print(le.tostring(doc))

yields

<root>
    <elm>Common content</elm>

    <elm>
        <elm>Content EN</elm>
        </elm>

    <elm>Common content</elm>

    <elm>Content EN</elm>
    <elm>
        <elm>Content EN</elm>
        <elm>Content EN</elm>
    </elm>

    </root>