Plugins

Beginning with version 3.0, Pelican supports plugins. Plugins are a way to add features to Pelican without having to directly modify the Pelican core.

How to use plugins

To load plugins, you have to specify them in your settings file. There are two ways to do so. The first method is to specify strings with the path to the callables:

PLUGINS = ['package.myplugin',]

Alternatively, another method is to import them and add them to the list:

from package import myplugin
PLUGINS = [myplugin,]

Note

When experimenting with different plugins (especially the ones that deal with metadata and content) caching may interfere and the changes may not be visible. In such cases disable caching with LOAD_CONTENT_CACHE = False or use the --ignore-cache command-line switch.

If your plugins are not in an importable path, you can specify a list of paths via the PLUGIN_PATHS setting. As shown in the following example, paths in the PLUGIN_PATHS list can be absolute or relative to the settings file:

PLUGIN_PATHS = ["plugins", "/srv/pelican/plugins"]
PLUGINS = ["assets", "liquid_tags", "sitemap"]

Where to find plugins

We maintain a separate repository of plugins for people to share and use. Please visit the pelican-plugins repository for a list of available plugins.

Please note that while we do our best to review and maintain these plugins, they are submitted by the Pelican community and thus may have varying levels of support and interoperability.

How to create plugins

Plugins are based on the concept of signals. Pelican sends signals, and plugins subscribe to those signals. The list of signals are defined in a subsequent section.

The only rule to follow for plugins is to define a register callable, in which you map the signals to your plugin logic. Let’s take a simple example:

from pelican import signals

def test(sender):
    print "%s initialized !!" % sender

def register():
    signals.initialized.connect(test)

Note

Signal receivers are weakly-referenced and thus must not be defined within your register callable or they will be garbage-collected before the signal is emitted.

List of signals

Here is the list of currently implemented signals:

Signal Arguments Description
initialized pelican object  
finalized pelican object invoked after all the generators are executed and just before pelican exits useful for custom post processing actions, such as: - minifying js/css assets. - notify/ping search engines with an updated sitemap.
generator_init generator invoked in the Generator.__init__
all_generators_finalized generators invoked after all the generators are executed and before writing output
readers_init readers invoked in the Readers.__init__
article_generator_context article_generator, metadata  
article_generator_preread article_generator invoked before a article is read in ArticlesGenerator.generate_context; use if code needs to do something before every article is parsed
article_generator_init article_generator invoked in the ArticlesGenerator.__init__
article_generator_pretaxonomy article_generator invoked before categories and tags lists are created useful when e.g. modifying the list of articles to be generated so that removed articles are not leaked in categories or tags
article_generator_finalized article_generator invoked at the end of ArticlesGenerator.generate_context
article_generator_write_article article_generator, content invoked before writing each article, the article is passed as content
article_writer_finalized article_generator, writer invoked after all articles and related pages have been written, but before the article generator is closed.
get_generators pelican object invoked in Pelican.get_generator_classes, can return a Generator, or several generators in a tuple or in a list.
get_writer pelican object invoked in Pelican.get_writer, can return a custom Writer.
page_generator_context page_generator, metadata  
page_generator_preread page_generator invoked before a page is read in PageGenerator.generate_context; use if code needs to do something before every page is parsed.
page_generator_init page_generator invoked in the PagesGenerator.__init__
page_generator_finalized page_generator invoked at the end of PagesGenerator.generate_context
page_writer_finalized page_generator, writer invoked after all pages have been written, but before the page generator is closed.
static_generator_context static_generator, metadata  
static_generator_preread static_generator invoked before a static file is read in StaticGenerator.generate_context; use if code needs to do something before every static file is added to the staticfiles list.
static_generator_init static_generator invoked in the StaticGenerator.__init__
static_generator_finalized static_generator invoked at the end of StaticGenerator.generate_context
content_object_init content_object invoked at the end of Content.__init__
content_written path, context invoked each time a content file is written.
feed_generated context, feed invoked each time a feed gets generated. Can be used to modify a feed object before it gets written.
feed_written path, context, feed invoked each time a feed file is written.

Warning

Avoid content_object_init signal if you intend to read summary or content properties of the content object. That combination can result in unresolved links when Linking to internal content (see pelican-plugins bug #314). Use _summary and _content properties instead, or, alternatively, run your plugin at a later stage (e.g. all_generators_finalized).

Note

After Pelican 3.2, signal names were standardized. Older plugins may need to be updated to use the new names:

Old name New name
article_generate_context article_generator_context
article_generate_finalized article_generator_finalized
article_generate_preread article_generator_preread
pages_generate_context page_generator_context
pages_generate_preread page_generator_preread
pages_generator_finalized page_generator_finalized
pages_generator_init page_generator_init
static_generate_context static_generator_context
static_generate_preread static_generator_preread

Recipes

We eventually realised some of the recipes to create plugins would be best shared in the documentation somewhere, so here they are!

How to create a new reader

One thing you might want is to add support for your very own input format. While it might make sense to add this feature in Pelican core, we wisely chose to avoid this situation and instead have the different readers defined via plugins.

The rationale behind this choice is mainly that plugins are really easy to write and don’t slow down Pelican itself when they’re not active.

No more talking — here is an example:

from pelican import signals
from pelican.readers import BaseReader

# Create a new reader class, inheriting from the pelican.reader.BaseReader
class NewReader(BaseReader):
    enabled = True  # Yeah, you probably want that :-)

    # The list of file extensions you want this reader to match with.
    # If multiple readers were to use the same extension, the latest will
    # win (so the one you're defining here, most probably).
    file_extensions = ['yeah']

    # You need to have a read method, which takes a filename and returns
    # some content and the associated metadata.
    def read(self, filename):
        metadata = {'title': 'Oh yeah',
                    'category': 'Foo',
                    'date': '2012-12-01'}

        parsed = {}
        for key, value in metadata.items():
            parsed[key] = self.process_metadata(key, value)

        return "Some content", parsed

def add_reader(readers):
    readers.reader_classes['yeah'] = NewReader

# This is how pelican works.
def register():
    signals.readers_init.connect(add_reader)

Adding a new generator

Adding a new generator is also really easy. You might want to have a look at Pelican internals for more information on how to create your own generator.

def get_generators(pelican_object):
    # define a new generator here if you need to
    return MyGenerator

signals.get_generators.connect(get_generators)