Exyr.org

I’m happy to announce the first release of tinycss! I captured it best in the README, so here it is:

tinycss is a complete yet simple CSS parser for Python. It supports the full syntax and error handling for CSS 2.1 as well as some CSS 3 modules:

• Selectors 3 (can also find matching elements in a lxml document)
• CSS Color 3
• CSS Paged Media 3

It is designed to be easy to extend for new CSS modules and syntax.

Quick facts:

• Free software: BSD licensed
• Compatible with Python 2.6+ and 3.x
• Latest documentation on python.org
• Source, issues and pull requests on Github
• Releases on PyPI
• Install with pip install tinycss

It now replaces cssutils in both WeasyPrint and CairoSVG. Sorry, Christof!

cssutils has served us very well. It allowed me to skip entire chapters of the CSS specifications when I started WeasyPrint a year ago, and get started quickly. The source is quite readable and well documented. cssutils is overall a very nice project.

However, patching cssutils to add support for the CSS 3 @page syntax turned out to be more painful than − I think − it should have been. The parser is somehow interleaved with the various data structures. cssutils also has some hard-to-fix performance issues. (Accessing a selector goes through the whole stylesheet every time to look for @namespace rules.)

So, as thankful as I am to Christof Höke for his work cssutils and for his support and collaboration with me, it was time for something simpler.

I started working on tinycss with a very clear idea of what I wanted: keep the implementation straightforward, and make it easy to extend for new syntax. After a few days of hacking I had a mostly working prototype that was already quite fast. I ended up adding optional Cython accelerators. The process of profiling and optimizing for speed was very interesting, but it is a whole other story.

This micro-benchmark (parsing and traversing a small stylesheet 20 times on my laptop) probably does not mean much, but the results certainly look nice:

$ python -m tinycss.tests.speed
tinycss + speedups        119 ms
tinycss WITHOUT speedups  174 ms  1.46x
cssutils                  928 ms  7.80x

As for extending, adding syntax is a matter of writing a subclass of CSS21Parser and overriding some methods. In fact, CSS 3 modules in tinycss are implemented precisely this way. Doing so ensure that extending is viable, and that the required hooks are included.

I then spent a lot more time getting the details right, polishing the API, writing documentation, and updating WeasyPrint to use this new parser. I’ve now got to a point where I am very satisfied with the project. From this 0.1 version, I will try not to change the user API without a good reason. (Although such reasons will probably come up sooner or later :)

For future versions I plan on adding parser support for Media Queries and CSS Namespaces, as well as maybe adding the selectors that are missing in lxml.cssselect.

I hope you’ll like cssutils too. Keep me posted if you do anything interesting with it (or any of my projects!) Have a look at the tinycss documentation and go from there.