dale lane

I need to diff some XML files.

For these particular XML files, order is not important. The XML is being used to contain a set of things, not a list – the order of the elements has no significance. Similarly, the order of the attributes within each element isn’t significant.

For example, for my purposes, these two XML files are equivalent:

<myroot>
    <mychild id="123">
        <fruit>apple</fruit>
        <test hello="world" brackets="angled" question="answers"/>
        <comment>This is a comment</comment>
    </mychild>
    <mychild id="456">
        <fruit>banana</fruit>
    </mychild>
    <mychild id="789">
        <fruit>orange</fruit>
        <test brackets="round" hello="greeting">
            <number>111</number>
        </test>
        <dates>
              <modified>123</modified>
              <created>253</created>
              <accessed>44</accessed>
        </dates>
    </mychild>
</myroot>

<myroot>
    <mychild id="789">
        <fruit>orange</fruit>
        <test hello="greeting" brackets="round">
            <number>111</number>
        </test>
        <dates>
              <accessed>44</accessed>    
              <modified>123</modified>
              <created>253</created>
        </dates>
    </mychild>
    <mychild id="123">
        <test question="answers" hello="world" brackets="angled"/>
        <comment>This is a comment</comment>
        <fruit>apple</fruit>
    </mychild>
    <mychild id="456">
        <fruit>banana</fruit>
    </mychild>
</myroot>

I needed to compare some large XML files, which have big differences in the order of elements, and I couldn’t find a tool that would do the job. So I wrote a bit of Python to do it for me.

How it works

I cheated.

Diff tools are complex, and I’m in a hurry without time to implement one.

Instead, to compare two of my XML files, my approach is to sort them both so they have a consistent order, and then diff the sorted files using an existing visual diff tool. (On Windows, I prefer vsdiff from SlickEdit. On Mac, I prefer diffmerge. My approach works with either of these.)

Example

For example, consider the following simple test files:

testA.xml

<myroot>
    <mychild id="123">
        <fruit>apple</fruit>
        <test hello="world" testing="removed" brackets="angled" question="answers"/>
        <comment>This is a comment</comment>
    </mychild>
    <mychild id="456">
        <fruit>banana</fruit>
        <comment>This will be removed</comment>
    </mychild>
    <mychild id="789">
        <fruit>orange</fruit>
        <test brackets="round" hello="greeting">
            <number>111</number>
        </test>
        <dates>
              <modified>123</modified>
              <created>880</created>
              <accessed>44</accessed>
        </dates>
    </mychild>
</myroot>

testB.xml

<myroot>
    <mychild id="789">
        <fruit>orange</fruit>
        <test hello="greeting" brackets="round">
            <number>111</number>
        </test>
        <dates>
              <accessed>49</accessed>    
              <modified>123</modified>
              <created>253</created>
        </dates>
    </mychild>
    <mychild id="123">
        <test question="answers" hello="world" brackets="angled"/>
        <comment>This is a comment</comment>
        <fruit>apple</fruit>
    </mychild>
    <mychild id="456">
        <fruit>banana</fruit>
    </mychild>
</myroot>

On Mac, I run:
$ python xmldiff.py diffmerge testA.xml testB.xml

And get:

On Windows, I run:
$ python xmldiff.py vsdiff testA.xml testB.xml

And get:

Source

The source showing how this works is available in a gist at
gist.github.com/dalelane.

It’s a quick hack to let me compare a handful of files, so it’s not been rigorously tested. But it’s a very simple little tool, and was good enough for my purposes tonight!

Tags: diff, python, xml

This entry was posted on Monday, October 6th, 2014 at 2:07 am and is filed under code. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.