Using SCons

Steven Lott

Sep. 02, 10 · News

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In looking at Application Lifecycle Management (see "ALM Tools"), I had found that SCons appears to be pretty popular. It's not as famous as all the make variants, or Apache Ant or Apache Maven, but it seems to have a niche in the forest of Build Automation Software.

While it looks nice, parts of SCons are confusing. I struggled until I found a simple use case.

More: Empirical Comparison of SCons and GNU Make.

"SCons proved to be more accurate, mostly due to its stateful, content-based signature model.

On the other hand, GNU Make proved to be more resource friendly, especially regard- ing the memory footprint. SCons needs to address this problem to be a viable alternative to Make when building large software projects."

[Also, it appears that a lot of build and test automation have been reframed as "Continuous Integration". Which isn't really a bad thing. But it can be confusing because there are too many categories into which general-purpose tools can be fit.]

While SCons looks cool, I haven't had a huge need for it at work. Working in Python, there's no real "build". Instead our continuous integration boils down to unit testing. Our "build" is an SVN checkin. Our deployment is an SVN checkout and `python setup.py install`.

At some point, I would like to create an SConstruct file that runs our integration test suite. But it's trapped at a low priority.

SCons and Sphinx

I did find an SConscript example that automated a document build using Sphinx. This

sphinx-scons was quite cool. However, it was challenging to customize. The SCons documentation requires real work to understand. I could see the value, but it was a lot of work.

I'm hoping that No Starch Press finds someone to write a tidy introduction to SCons.

SCons and RST and LaTeX (oh, my!)

Sphinx has made me a total fanboi of ReStructured Text. While I know MS Word and iWorks Pages quite well, I have no patience with all the pointing and clicking. Getting consistency is requires consistent pointing and clicking; some people can do it, but some of us find that manual pointing and clicking is sometimes irreproducible. Semantic markup is a huge pain in the neck because we have to stop typing to click on the proper style hint for the various words.

I also know DocBook XML and LaTeX quite well. I've used very cool XML editors including XML Mind XML Editor (which is very nice.) I no longer have any patience with any of these tools because there's too much GUI.

RST is fun because you write in plain text. There are a few directives and a few bits of inline roles for semantic markup. But your work can focus on the content, leaving presentation aside. A command-line tool (with templates) emits HTML or LaTeX or whatever. The style considerations can be (a) secondary and (b) completely consistent.

RST will easily produce complex LaTeX from plain text. What a joy. LaTeX, of course, isn't the goal, it's just an intermediate result that leads to DVI which leads -- eventually -- to a PDF.

Because of the Unicode and font selection on the Mac, I'm a user of XeTeX and XeLaTeX. I have some problems with getting my copy of Blackadder ITC to work, but generally I'm able to write without much fussing around.

SCons has a great deal of the TeX/DVI/PDF tool chain already installed. However, it doesn't have either the rst2latex script or the XeTeX tools.

An SConscript

While my first attempts to understand SCons didn't work out well, looking at RST and XeLaTex was a much better use case.

I wound up with this.

rst2latex = Builder( action="rst2latex.py $SOURCES >$TARGET",
suffix='.tex', src_suffix='.rst',
)
xelatex = Builder( action=["xelatex $SOURCES", "xelatex $SOURCES"],
suffix='.pdf', src_suffix='.tex',
)
env = Environment(ENV=os.environ,
BUILDERS = { 'rst2latex' : rst2latex, 'xelatex':xelatex }
)

env.rst2latex('someDoc')
env.xelatex('someDoc' )
env.rst2latex('anotherDoc')
env.xelatex('anotherDoc')

Getting this to work was quite pleasant. I can see how I could further optimize the document production pipeline by combining the two Builders.

[And yes, the xelatex step is run twice to guarantee that the references are correct.]

Now, I can get away with write, run `scons` and review the resulting PDF. It's fast and it produces a nice-looking PDF with very little work and no irreproducible pointing and clicking.

Given this baseline, I can now dig into SCons for ways to make this slightly simpler.

Continuous Integration/Deployment

Published at DZone with permission of Steven Lott, DZone MVB. See the original article here.

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