---
author: ''
category: ''
date: 2012/08/10 20:06:54
description: ''
link: ''
priority: ''
slug: nikola-filters-bundles
tags: nikola, python
title: 'Nikola: Filters & Bundles'
type: text
updated: 2012/08/10 20:06:54
url_type: ''
---
Two upcoming features for the next release of `Nikola <http://nikola.ralsina.coma.r>`_,
my static site generator, due sometime in August.

Filters
-------

Filters let you postprocess your output. Think of it like instagram for
websites, but useful. You can configure per file extension a series
of python functions or shell commands, which will be applied in place
to the output file.

For example, suppose you want to apply yui-compressor to your CSS and JS
files:

.. code-block:: python

    FILTERS = {
        ".css": [filters.yui_compressor],
        ".js": [filters.yui_compressor],
    }

There, ``filters.yui_compressor`` is a simple wrapper around the command
so that it applies in-place to the output files.

If you use strings there (untested), they are taken as commands. The "%s" will
be replaced by the filename, the usual crazy shell quoting
rules apply:

.. code-block:: python

    FILTERS = {
        ".jpg": ["jpegoptim '%s'"],
        ".png": ["pngoptim '%s'"],
    }

Keep in mind that the filters modify the *output* of Nikola, not the input, so
your images, CSS, and JS files will not be touched in any way. And of course
changing the filters applied to a file will force a rebuild, so you can
experiment freely.

Bundles
-------

Having many separate CSS or JS files is usually a nono for performance reasons
because each one may involve a separate HTTP transaction. The solution is to
"bundle" those files in a single, larger file.

The reason not to do that is that usually it means having a huge, uncomfortable
thing to handle. So Nikola tries to give you the best of both worlds, by letting
you have separate files, and bundling them (or not) on build.

There is a new option, ``USE_BUNDLES`` that defaults to False, and there are
some changes in the theme templates so that it uses the bundled version when
needed.

This was only possible thanks to `Webassets <http://webassets.readthedocs.org/>`_.
However, if you don't have Webassets installed, or you don't enable USE_BUNDLES,
this should cause no changes in the output.

Conclusion
----------

These new features will allow Nikola users to improve their site's performance
with minimal tweaking, which is always a good thing.