# Hooks¶

Although Acrylamid supports many libraries and external tools, it is rather limited due the simple configration syntax. To extend the compilation process, Acrylamid allows you to hook into its events (create, update and so on). This allows you to do something witht the generated files, for example generating image thumbnails on-the-fly and/or compress the produced HTML.

By default, all hooks are executed in parallel (not affected by the GIL if you run external processes/commands), you can disable this behavior by setting HOOKS_MT to False.

There are two different types of hooks. The simple hook “listens” on the create and update events and simply calls your function with the namespace [#1] of the event and the path, in this order. Whereas the advanced hook hooks into all available event types but requires a path translation function to automatically determine whether the callback should be executed or not.

Instead of writing callbacks in Python, you can also supply a shell command with one (simple) or two (advanced) arguments. The namespace is not available within shell commands.

from os.path import join, dirname, basename

HOOKS = {
# stdout is written to a temporary file and then moved to %1
'.+\.html': 'htmlcompressor %1',

# with path translation, you have src and dest (%1 and %2)
'.+\.jpg' : (
'convert -thumbnail 150x150^ -gravity center -extent 150x150 %1 %2',
lambda p: lambda p: join(dirname(p), 'thumbs/', basename(p))
)
}

 [1] the namespace indicates the originator of the event. It can be on of the following: archive, articles, entry, feeds, index, sitemap, tag, assets or None.

## Simple Hook¶

The simplest hook is just a function that receives original namespace and path from the event utility. You have more freedom, but it may have an impact to compilation speed if not implemented correctly.

def doit(namespace, path):

# namespace -> assets, entry and so on.
# path -> output/path/to/file
pass

HOOKS = {
'.+\.html': doit
}


An advanced hook is less readable than the naive, but tightlier integrated into Acrylamid’s modification detection mechanisms. You need to provide your function as in the naive hook and additionally a path translation function. The path translation helps Acrylamid to determine whether it is necessary to execute the hook or not.

from acrylamid import log
from acrylamid.helpers import system, AcrylamidException
from os import makedirs
from os.path import exists, dirname, basename, join

def mkthumb(ns, src, dest):
if not exists(dirname(dest)):
makedirs(dirname(dest))
try:
system(['convert',
'-define', 'jpeg:size=320x320',
'-thumbnail', '160x160^',
'-gravity', 'center',
'-extent', '160x160',
src, dest])
except AcrylamidException as e:
log.warn(e.args[0])
except OSError:
pass
else:
log.info('create  thumbnail  %s', dest)

HOOKS = {
'images/.+\.(jpg|png)': (
mkthumb,
lambda p: join(dirname(p), 'thumbs/', basename(p))
),
}


The hook above will create thumbnails on-the-fly using Imagemagick’s convert and saves these thumbnails to a dedicated thumbs/ folder.