Extending Nikola

Command Plugins

When you run nikola --help you will see something like this:

$ nikola help
Nikola is a tool to create static websites and blogs. For full documentation and more
information, please visit http://getnikola.com


Available commands:
nikola auto                 automatically detect site changes, rebuild
                            and optionally refresh a browser
nikola bootswatch_theme     given a swatch name from bootswatch.com and a
                            parent theme, creates a custom theme
nikola build                run tasks
nikola check                check links and files in the generated site
nikola clean                clean action / remove targets
nikola console              start an interactive python console with access to
                            your site and configuration
nikola deploy               deploy the site
nikola dumpdb               dump dependency DB
nikola forget               clear successful run status from internal DB
nikola help                 show help
nikola ignore               ignore task (skip) on subsequent runs
nikola import_blogger       import a blogger dump
nikola import_feed          import a RSS/Atom dump
nikola import_wordpress     import a WordPress dump
nikola init                 create a Nikola site in the specified folder
nikola install_theme        install theme into current site
nikola list                 list tasks from dodo file
nikola mincss               apply mincss to the generated site
nikola new_post             create a new blog post or site page
nikola run                  run tasks
nikola serve                start the test webserver
nikola strace               use strace to list file_deps and targets
nikola version              print the Nikola version number

nikola help                 show help / reference
nikola help <command>       show command usage
nikola help <task-name>     show task usage

That will give you a list of all available commands in your version of Nikola. Each and every one of those is a plugin. Let's look at a typical example:

First, the command_serve.plugin file:

[Core]
Name = serve
Module = serve

[Documentation]
Author = Roberto Alsina
Version = 0.1
Website = http://getnikola.com
Description = Start test server.

For your own plugin, just change the values in a sensible way. The Module will be used to find the matching python module, in this case serve.py, from which this is the interesting bit:

from nikola.plugin_categories import Command

# You have to inherit Command for this to be a
# command plugin:

class CommandBuild(Command):
    """Start test server."""

    name = "serve"
    doc_usage = "[options]"
    doc_purpose = "start the test webserver"

    cmd_options = (
        {
            'name': 'port',
            'short': 'p',
            'long': 'port',
            'default': 8000,
            'type': int,
            'help': 'Port nummber (default: 8000)',
        },
        {
            'name': 'address',
            'short': 'a',
            'long': '--address',
            'type': str,
            'default': '127.0.0.1',
            'help': 'Address to bind (default: 127.0.0.1)',
        },
    )

    def _execute(self, options, args):
        """Start test server."""
        out_dir = self.site.config['OUTPUT_FOLDER']
        if not os.path.isdir(out_dir):
            print("Error: Missing '{0}' folder?".format(out_dir))
        else:
            os.chdir(out_dir)
            httpd = HTTPServer((options['address'], options['port']),
                            OurHTTPRequestHandler)
            sa = httpd.socket.getsockname()
            print("Serving HTTP on", sa[0], "port", sa[1], "...")
            httpd.serve_forever()

As mentioned above, a plugin can have options, which the user can see by doing nikola help command and can later use, for example:

$ nikola help serve
Purpose: start the test webserver
Usage:   nikola serve [options]

Options:
-p ARG, --port=ARG        Port nummber (default: 8000)
-a ARG, ----address=ARG   Address to bind (default: 127.0.0.1)

$ nikola serve -p 9000
Serving HTTP on 127.0.0.1 port 9000 ...

So, what can you do with commands? Well, anything you want, really. I have implemented a sort of planet using it. So, be creative, and if you do something interesting, let me know ;-)

TemplateSystem Plugins

Nikola supports Mako and Jinja2. If you prefer some other templating system, then you will have to write a TemplateSystem plugin. Here's how they work. First, you have to create a .plugin file. Here's the one for the Mako plugin:

[Core]
Name = mako
Module = mako

[Documentation]
Author = Roberto Alsina
Version = 0.1
Website = http://getnikola.com
Description = Support for Mako templates.

You will have to replace "mako" with your template system's name, and other data in the obvious ways.

The "Module" option is the name of the module, which has to look something like this, a stub for a hypothetical system called "Templater":

from nikola.plugin_categories import TemplateSystem

# You have to inherit TemplateSystem

class TemplaterTemplates(TemplateSystem):
    """Wrapper for Templater templates."""

    # name has to match Name in the .plugin file
    name = "templater"

    # You *must* implement this, even if to return []
    # It should return a list of all the files that,
    # when changed, may affect the template's output.
    # usually this involves template inheritance and
    # inclusion.
    def get_deps(self, filename):
        return []

    # A list of directories where the templates will be
    # located. Most template systems have some sort of
    # template loading tool that can use this.

    def set_directories(self, directories):
        """Create a template lookup."""
        pass

    # The method that does the actual rendering.
    # template_name is the name of the template file,
    # output_name is the file for the output, context
    # is a dictionary containing the data the template
    # uses for rendering.

    def render_template(self, template_name, output_name,
        context, global_context):
        """Render the template into output_name using context."""
        pass

Task Plugins

If you want to do something that depends on the data in your site, you probably want to do a Task plugin, which will make it be part of the nikola build command. There are the currently available tasks, all provided by plugins:

$ nikola list
Scanning posts....done!
build_bundles
build_less
copy_assets
copy_files
post_render
redirect
render_archive
render_galleries
render_galleries_clean
render_indexes
render_listings
render_pages
render_posts
render_rss
render_site
render_sources
render_tags
sitemap

These have access to the site object which contains your timeline and your configuration.

The critical bit of Task plugins is their gen_tasks method, which yields doit tasks

The details of how to handle dependencies, etc. are a bit too much for this document, so I'll just leave you with an example, the copy_assets task. First the task_copy_assets.plugin file, which you should copy and edit in the logical ways:

[Core]
Name = copy_assets
Module = task_copy_assets

[Documentation]
Author = Roberto Alsina
Version = 0.1
Website = http://getnikola.com
Description = Copy theme assets into output.

And the task_copy_assets.py file, in its entirety:

import os

from nikola.plugin_categories import Task
from nikola import utils

# Have to inherit Task to be a task plugin
class CopyAssets(Task):
    """Copy theme assets into output."""

    name = "copy_assets"

    # This yields the tasks
    def gen_tasks(self):
        """Create tasks to copy the assets of the whole theme chain.

        If a file is present on two themes, use the version
        from the "youngest" theme.
        """

        # I put all the configurations and data the plugin uses
        # in a dictionary because utils.config_changed will
        # make it so that if these change, this task will be
        # marked out of date, and run again.

        kw = {
            "themes": self.site.THEMES,
            "output_folder": self.site.config['OUTPUT_FOLDER'],
            "filters": self.site.config['FILTERS'],
        }

        tasks = {}
        for theme_name in kw['themes']:
            src = os.path.join(utils.get_theme_path(theme_name), 'assets')
            dst = os.path.join(kw['output_folder'], 'assets')
            for task in utils.copy_tree(src, dst):
                if task['name'] in tasks:
                    continue
                tasks[task['name']] = task
                task['uptodate'] = task.get('uptodate', []) + \
                    [utils.config_changed(kw)]
                task['basename'] = self.name
                # If your task generates files, please do this.
                yield utils.apply_filters(task, kw['filters'])

PageCompiler Plugins

These plugins implement markup languages, they take sources for posts or pages and create HTML or other output files. A good example is the misaka plugin.

They must provide:

compile_html

Function that builds a file.

create_post

Function that creates an empty file with some metadata in it.

If the compiler produces something other than HTML files, it should also implement extension which returns the preferred extension for the output file.

RestExtension Plugins

Implement directives for reStructuredText, see media.py for a simple example.

SignalHandler Plugins

These plugins extend the SignalHandler class and connect to one or more signals via blinker

The easiest way to do this is to reimplement set_site() and just connect to whatever signals you want there.

Currently Nikola emits the following signals:

sighandlers_loaded

Right after SignalHandler plugin activation.

initialized

Right after plugin activation

configured

When all the configuration file is processed. Note that plugins are activated before this is emitted.

new_post

When a new post is created, using the nikola new_post command. The signal data contains the path of the file, and the metadata file (if there is one).

deployed

When the nikola deploy command is run, and there is at least one new entry/post since last_deploy. The signal data is of the form

{
 'last_deploy: # datetime object for the last deployed time,
 'new_deploy': # datetime object for the current deployed time,
 'clean': # whether there was a record of a last deployment,
 'deployed': # all files deployed after the last deploy,
 'undeployed': # all files not deployed since they are either future posts/drafts
}