xml_diff

Compares the text inside two XML documents and marks up the differences with <del> and <ins> tags.

This is the result of about 7 years of trying to get this right and coded simply. I’ve used code like this in one form or another to compare bill text on GovTrack.us <https://www.govtrack.us>.

The comparison is completely blind to the structure of the two XML documents. It does a word-by-word comparison on the text content only, and then it goes back into the original documents and wraps changed text in new <del> and <ins> wrapper elements.

The documents are then concatenated to form a new document and the new document is printed on standard output. Or use this as a library and call compare yourself with two lxml.etree.Element nodes (the roots of your documents).

The script is written in Python 3 and uses Google’s Diff Match Patch library <https://code.google.com/p/google-diff-match-patch/>, as re-written and sped-up by @leutloff <https://github.com/leutloff/diff-match-patch-cpp-stl> and then turned into a Python extension module by me <https://github.com/JoshData/diff_match_patch-python>. (A great pull request would be to replace that dependency with Python’s built-in difflib <https://docs.python.org/3/library/difflib.html> module. It’ll be slower but then won’t have any unusual dependencies.)

<html>
        Here is <b>some bold</b> text.
</html>

<html>
        Here is <i>some italic</i> content that shows how <tt>xml_diff</tt> works.
</html>

<documents>
        <html>
                Here is <b>some <del>bold</del></b><del> text</del>.
        </html>
        <html>
                Here is <i>some <ins>italic</ins></i><ins> content that shows how </ins><tt><ins>xml_diff</ins></tt><ins> works</ins>.
        </html>
</documents>

sudo apt-get install python3-lxml
# or
sudo apt-get install libxml2-dev libxslt1-dev
sudo pip3 install lxml

# get my Python extension module for the Google Diff Match Patch library
# so we can compute differences in text very quickly
git clone --recursive https://github.com/JoshData/diff_match_patch-python
cd diff_match_patch-python
sudo apt-get install python3-dev
python3 setup.py build
sudo python3 setup.py install

python3 xml_diff.py --tags del,ins doc1.xml doc2.xml > with_changes.xml