Question

I’m writing an application configuration module that uses XML in its files. Consider the following example:

<?xml version="1.0" encoding="UTF-8"?>
<Settings>
    <PathA>/Some/path/to/directory</PathA>
    <PathB>/Another/path</PathB>
</Settings>

Now, I’d like to override certain elements in a different file that gets loaded afterwards. Example of the override file:

<?xml version="1.0" encoding="UTF-8"?>
<Settings>
    <PathB>/Change/this/path</PathB>
</Settings>

When querying the document (with overrides) with XPath, I’d like to get this as the element tree:

<?xml version="1.0" encoding="UTF-8"?>
<Settings>
    <PathA>/Some/path/to/directory</PathA>
    <PathB>/Change/this/path</PathB>
</Settings>

This is similar to what Python’s ConfigParser does with its read() method, but done with XML. How can I implement this?

Answer 1

You could convert the XML into an instance of Python class:

import lxml.etree as ET
import io

class Settings(object):
    def __init__(self,text):
        root=ET.parse(io.BytesIO(text)).getroot()
        self.settings=dict((elt.tag,elt.text) for elt in root.xpath('/Settings/*'))
    def update(self,other):
        self.settings.update(other.settings)

text='''\
<?xml version="1.0" encoding="UTF-8"?>
<Settings>
    <PathA>/Some/path/to/directory</PathA>
    <PathB>/Another/path</PathB>
</Settings>'''

text2='''\
<?xml version="1.0" encoding="UTF-8"?>
<Settings>
    <PathB>/Change/this/path</PathB>
</Settings>'''    

s=Settings(text)
s2=Settings(text2)
s.update(s2)
print(s.settings)

yields

{'PathB': '/Change/this/path', 'PathA': '/Some/path/to/directory'}