Adding XML data from a XML file to an existing XML file

Question

I'm very new to Python, only read the Learn Python the Hard Way. But I think this is still way out of my scope. My skills are in XML/XSL, not Python. I need a little help to get started.

Overview: I need to add missing XML data (addition.xml) into a existing XML file (original.xml).

XML file (with the data that is missing): (addition.xml)

<profile>
    <dog-list>
        <dog>
            <name>sally</dog>
            <age>1</age>
        </dog>
        <dog>
            <name>susie</dog>
            <age>12</age>
        </dog>
    </dog-list>
    <people-list>
        <person>
            <name>ue</name>
            <age>25</age>
            <gender>female</gender>
        </person>
    </people-list>
</profile>

XML data above adds to this XML file: (original.xml)

<profile>
    <cat-list>
        <cat>
            <name>foo></name>
        </cat>
        <cat>
            <name>bar</name>
            <age>3</age>
        </cat>
    </cat-list>
    <bird-list>
        <bird>
            <name>cricket</name>
            <age>2</age>
        </bird>
    </bird-list>
    <people-list>
        <person>
            <name>tyler</name>
            <age>26</age>
        </person>
    </people-list>
    <car-list>
        <car>
            <make>mitsubishi</make>
            <model>evo x</model>
            <year>2013</year>
        </car>
    </car-list>
</profile>

My expected output should be: --> the new (original.xml)

<profile>
    <cat-list>
        <cat>
            <name>foo></name>
        </cat>
        <cat>
            <name>bar</name>
            <age>3</age>
        </cat>
    </cat-list>
    <dog-list>
        <dog>
            <name>sally</dog>
            <age>1</age>
        </dog>
        <dog>
            <name>susie</dog>
            <age>12</age>
        </dog>
    </dog-list>
    <bird-list>
        <bird>
            <name>cricket</name>
            <age>2</age>
        </bird>
    </bird-list>
    <people-list>
        <person>
            <name>tyler</name>
            <age>26</age>
        </person>
        <person>
            <name>ue</name>
            <age>25</age>
            <gender>female</gender>
        </person>
    </people-list>
    <car-list>
        <car>
            <make>mitsubishi</make>
            <model>evo x</model>
            <year>2013</year>
        </car>
    </car-list>
</profile>

What happens here is that data from the addition.xml is missing from the original.xml file. How do I go about adding data from addition.xml into the original.xml instead of creating a new file, overwriting it.

I look all over google and stackoverflow. I know that I could use ElementTree but I have the foggiest idea how to create this result.

Any help is greatly appreciated!

Answer 1

Your requirements don't allow a general-purpose merge program (like the one you link to), but here is a program that might work for you.

Usage: ./program.py original.xml addition.xml

#! /usr/bin/python2

import sys
from lxml import etree

result = etree.Element('root')
parser = etree.XMLParser(remove_blank_text=True)

# Add each file to the tree
for xmlfile in sys.argv[1:]:
  with open(xmlfile) as xmlfile:
    btree = etree.parse(xmlfile, parser)
  # Ensure that the resulting tree has the right root
  result.tag = btree.getroot().tag
  # Consider each 2nd-level item
  for bchild in btree.xpath("/*/*"):
    tags = result.xpath("./%s"%bchild.tag)
    if len(tags) == 0:
      # Add <dog-list>, for example
      #print "adding %s to %s"%(bchild.tag, result.tag)
      result.append(bchild)
    else:
      for bgrandchild in bchild:
        # add <dog>, for example
        #print "adding %s to %s"%(bgrandchild.tag, tags[0].tag)
        tags[0].append(bgrandchild)

with open("output.xml", "w") as output:
  output.write(etree.tostring(result, pretty_print = True))