Compares two XML documents by diffing their text, ignoring structure, and wraps changed text in <del>/<ins> tags.
Project description
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. The module works with any Google Diff Match Patch-compatible differencing library. You provide it a differ function which takes two strings and returns a list of (op, length) tuples, where op is “+” (insertion), “-” (deletion), or “0” (no change). If will use my extension module <https://github.com/JoshData/diff_match_patch-python> if it is available, falling back on the pure-Python <https://code.google.com/p/google-diff-match-patch/source/browse/trunk/python3/diff_match_patch.py> if it is available, or else the not very useful Python built-in difflib.
Example
Comparing these two documents:
<html>
Here is <b>some bold</b> text.
</html>
and:
<html>
Here is <i>some italic</i> content that shows how <tt>xml_diff</tt> works.
</html>
Yields:
<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>
First install the module:
pip install xml_diff
On Ubuntu, apt-get installing python3-lxml or libxml2-dev and libxslt1-dev might be necessary. When installing from source, you’ll need lxml too (but pip will get it for you automatically).
Then call the module from the command line:
python -m xml_diff --tags del,ins doc1.xml doc2.xml > changes.xml
For really fast comparisons, get 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>:
pip install diff_match_patch_python
The command-line tool (above) will use this library if it is available.
Use the module from Python like so:
import lxml.etree
from xml_diff import compare
dom1 = lxml.etree.parse("doc1.xml").getroot()
dom2 = lxml.etree.parse("doc2.xml").getroot()
compare(dom1, dom2)
The two DOMs are modified in-place.
If you can’t install diff_match_patch_python, you can also get the pure-Python version of diff_match_patch.py from <https://code.google.com/p/google-diff-match-patch/source/browse/trunk/python3/diff_match_patch.py>. (The command-line tool will fall back to this library if it is available.)
Or you can pass in your own comparison library as the third argument. (See xml_diff/__init__.py’s default_differ function for how it would work.)
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