Contributing to xmldiff

xmldiff welcomes your help. Replies and responses may be slow, but don’t despair, we will get to you, we will answer your questions and we will review your pull requests, but nobody has “Maintain xmldiff” as their job description, so it may take a long time. That’s open source.

There are some extremely complex issues deep down in xmldiff, but don’t let that scare you away, there’s easy things to do as well.

Setting Up a Development Environment

To set up a development environment you need a github account, git, and of course Python with pip installed. You also should have the Python tools coverage and flake8 installed:

pip install coverage flake8

Then you need to clone the repository, and install it’s dependencies:

git clone
cd xmldiff
pip install -e .

You should now be able to test your setup by running a few make commands:

make test
make flake

These should both pass with no errors, and then you are set!


xmldiff’s tests are written using unittest and are discoverable by most test runners. There is also a test target in the make file. The following test runners/commands are known to work:

  • make test
  • python test
  • nosetests
  • pytest

There is no support for tox to run test under different Python versions. This is because Travis will run all supported versions on pull requests in any case, and having yet another list of supported Python versions to maintain seems unnecessary. You can either create your own tox.ini file, or you can install Spiny, which doesn’t require any extra configuration in the normal case, and will run the tests on all versions that are defined as supported in

Pull Requests

Even if you have write permissions to the repository we discourage pushing changes to master. Make a branch and a pull request, and we’ll merge that.

You pull requests should:

  • Add a test that fails before the change is made
  • Keep test coverage at 100%
  • Include an description of the change in CHANGES.txt
  • Add yourself to the contributors list in README.txt if you aren’t already there.

Code Quality and Conventions

xmldiff aims to have 100% test coverage. You run a coverage report with make coverage. This will generate a HTML coverage report in htmlcov/index.html

We run flake8 as a part of all Travis test runs, the correct way to run it is make flake, as this includes only the files that should be covered.


The documentation is written with sphinx. It and any other files using the ReStructuredText format, such as README’s etc, are using a one line per sub-sentence structure. This is so that adding one word to a paragraph will not cause several lines of changes, as that will make any pull request harder to read.

That means that every sentence and most commas should be followed by a new line, except in cases where this obviously do not make sense, for example when using commas to separate things you list. As a result of this there is no limits on line length, but if a line becomes very long you might consider rewriting it to make it more understandable.

You generate the documentation with a make command:

cd docs
make html

The documentation is hosted on Read the Docs, the official URL is

Implementation Details

xmldiff is based on “Change Detection in Hierarchically StructuredS Information” by Sudarshan S. Chawathe, Anand Rajaraman, Hector Garcia-Molina, and Jennifer Widom, 1995. It’s not necessary to read and understand that paper in all it’s details to help with xmldiff, but if you want to improve the actual diffing algorithm it is certainly helpful.

I hope to extend this section with an overview of how this library does it’s thing.