Patch the difference of two XML instance files into the template XML file

Question

I have a template XML file written using mako engine which is used to generate a config XML file. Below is a sample template.

<?xml version="1.0"?>
<data>
    <country name="Liechtenstein">
        <rank>${rank}</rank>
        <year>2008</year>
        % if gdppc:
        <gdppc>${gdppc}</gdppc>
        % endif
        <neighbor name="Austria" direction="E"/>
        <neighbor name="Switzerland" direction="W"/>
    </country>
</data>

A config file is generated using the template, as shown below. Call it version 1.

<?xml version="1.0"?>
<data>
    <country name="Liechtenstein">
        <rank>1</rank>
        <year>2008</year>
        <gdppc>141100</gdppc>
        <neighbor name="Austria" direction="E"/>
        <neighbor name="Switzerland" direction="W"/>
    </country>
</data>

New changes are made to the config file that might look like this. Call it version 2. Changes could be modification to nodes, tags, attributes, etc.

<data>
    <country name="Liechtenstein">
        <rank>1</rank>
        <year>2009</year>
        <gdppc>141100</gdppc>
        <neighbour name="Austria" direction="E"/>
    </country>
</data>

Now how do I identify the new changes and patch them into the template? Or what is the right approach to update template files given the changes?

I have tried using xmldiff to extract and patch the changes into the template, but there are two problems when using it.

• xmldiff generates numerous unwanted changes when used with large XML config files.
• Patching into the template is not the best approach as the mako templates are not natively supported.