Monday, March 29, 2010

Blogging with reStructuredText and Pygments

I have been syntax highlighting my code in these blog posts using syntaxhighlighter. I am encountering two problems with this:

  1. I am relying on an external service to source the javascript providing the functionality. This hasn't been a problem to date, but it is a point of failure and is occasionally slow.
  2. The code isn't being shown in the RSS feed for this site.

An alternative approach is to convert the code directly to syntax highlighted HTML and paste the resulting content directly into my blog entries. This is a small part of Doug Hellman's workflow for writing technical documentation.

I don't (yet) need the complete workflow described by Doug. I just need the reStructuredText and Pygments capabilities for now. This post is the first output from this process.

Installing reStructuredText and Pygments is quite simple using easy_install. The docutils package provides reStructuredText tools and is installed by typing the following at a terminal prompt:

easy_install -U docutils

You might need an sudo at the front of that line to get some of the tools installed in system directories. With docutils installed you can start writing reST documents and have the tools to turn them into HTML, LaTeX and others formats. See the reStructuredText website for more information. Pygments provides source code syntax highlighting and is installed similarily to docutils:

easy_install -U pygments

A command line program pygmentize will be installed and can be used to manually turn source code into highlighted text in a number of formats including HTML. Consult the Pygments website for more information.

True documenting power comes from being able to include source code within a reST document and have Pygments automatically highlight the code. Getting this to work, however, is a little fiddly. Below is the sequence of steps I took to get this working.

  1. Obtain the from Pygments. I couldn't find this on my system and ended up cloning the Pygments Mercurial repository and grabbing the file from the external directory. The repository can be cloned using the command:

    hg clone pygments
  2. Follow the instructions for registering a directive. The docutils/parsers/rst/directives directory is located within /Library/Python/2.6/site-packages on my Snow Leopard Macbook. I renamed the file to within the directives directory and add the entry 'sourcecode':('sourcecode', 'Pygments') to the _directive_registry dictionary.

Update: I've now updated my docutils install (using easy_install -U docutils) to version 0.7. This appears to break the sourcecode directive installed using the previous instruction. It seems that version 0.7 is installed into a version specific directory within /Library/Python/2.6/site-packages. The directory is named docutils-0.7-py2.6.egg and within which are the directories mentioned above into which the sourcecode directive can be installed. After installing in this new directory my HTML generation was once again successful with regard to the source code blocks.

  1. Pygments wraps various parts of source code with span tags when generating HTML. These span tags are assigned a class and these classes are styled using CSS. The style used by Pygments can be written to file using the command line pygmentize -S default -f html -a .highlight > style.css. The .highlight corresponds to the highlight class assigned to the div surrounding the entire source code block. Specifying this ensures the Pygments specific CSS classes are only applied to elements within this top level div. Add the content of style.css to my Blogger template so that any Pygment generated HTML that I paste in will be correctly coloured.

All that is required now is to add some source code. Here is Hello World (what else) in C++.

#include <iostream>

int main(int argc, const char* argv[])
  std::cout << "Hello World!" << std::endl;

  return 0;

Typeset this using rst2html:

rst2html input.rst > output.html

and then copy the body content of output.html to Blogger as a new post.


pygabriel said...

Thank you very much for the article it's pretty complete and nice, I will use rest+pygments to format my articles now!

Anthony said...

Glad you found it useful.

Sorry for not replying until now. I hadn't setup email notifications for comments.