elstir Plugins 

A Guide to installing, using and creating elstir Plugins

Installing Plugins

Before a plugin can be used, it must be installed on the system. If you are using a plugin which comes with elstir, then it was installed when you installed elstir. However, to install third party plugins, you need to determine the appropriate package name and install it using pip:

pip install elstir-foo-plugin

Once a plugin has been successfully installed, it is ready to use. It just needs to be enabled in the configuration file. The elstir Plugins wiki page has a growing list of plugins that you can install and use.

Using Plugins

The plugins configuration option should contain a list of plugins to use when building the site. Each "plugin" must be a string name assigned to the plugin (see the documentation for a given plugin to determine its "name"). A plugin listed here must already be installed.

plugins:
    - search

Some plugins may provide configuration options of their own. If you would like to set any configuration options, then you can nest a key/value mapping (option_name: option value) of any options that a given plugin supports. Note that a colon (:) must follow the plugin name and then on a new line the option name and value must be indented and separated by a colon. If you would like to define multiple options for a single plugin, each option must be defined on a separate line.

plugins:
    - search:
        lang: en
        foo: bar

For information regarding the configuration options available for a given plugin, see that plugin's documentation.

For a list of default plugins and how to override them, see the configuration documentation.

Developing Plugins

Like elstir, plugins must be written in Python. It is generally expected that each plugin would be distributed as a separate Python module, although it is possible to define multiple plugins in the same module. At a minimum, a elstir Plugin must consist of a BasePlugin subclass and an entry point which points to it.

BasePlugin

A subclass of elstir.plugins.BasePlugin should define the behavior of the plugin. The class generally consists of actions to perform on specific events in the build process as well as a configuration scheme for the plugin.

All BasePlugin subclasses contain the following attributes:

config_scheme

A tuple of configuration validation instances. Each item must consist of a two item tuple in which the first item is the string name of the configuration option and the second item is an instance of elstir.config.config_options.BaseConfigOption or any of its subclasses.

For example, the following config_scheme defines three configuration options: foo, which accepts a string; bar, which accepts an integer; and baz, which accepts a boolean value.

class MyPlugin(elstir.plugins.BasePlugin):
    config_scheme = (
        ('foo', elstir.config.config_options.Type(str, default='a default value')),
        ('bar', elstir.config.config_options.Type(int, default=0)),
        ('baz', elstir.config.config_options.Type(bool, default=True))
    )

When the user's configuration is loaded, the above scheme will be used to validate the configuration and fill in any defaults for settings not provided by the user. The validation classes may be any of the classes provided in elstir.config.config_options or a third party subclass defined in the plugin.

Any settings provided by the user which fail validation or are not defined in the config_scheme will raise a elstir.config.base.ValidationError.

config

A dictionary of configuration options for the plugin, which is populated by the load_config method after configuration validation has completed. Use this attribute to access options provided by the user.

def on_pre_build(self, config):
    if self.config['bool_option']:
        # implement "bool_option" functionality here...

All BasePlugin subclasses contain the following method(s):

load_config(options)

Loads configuration from a dictionary of options. Returns a tuple of (errors, warnings). This method is called by elstir during configuration validation and should not need to be called by the plugin.

on_<event_name>()

Optional methods which define the behavior for specific events. The plugin should define its behavior within these methods. Replace <event_name> with the actual name of the event. For example, the pre_build event would be defined in the on_pre_build method.

Most events accept one positional argument and various keyword arguments. It is generally expected that the positional argument would be modified (or replaced) by the plugin and returned. If nothing is returned (the method returns None), then the original, unmodified object is used. The keyword arguments are simply provided to give context and/or supply data which may be used to determine how the positional argument should be modified. It is good practice to accept keyword arguments as **kwargs. In the event that additional keywords are provided to an event in a future version of elstir, there will be no need to alter your plugin.

For example, the following event would add an additional static_template to the theme config:

class MyPlugin(BasePlugin):
    def on_config(self, config, **kwargs):
        config['theme'].static_templates.add('my_template.html')
        return config

Events

There are three kinds of events: Global Events, Page Events and Template Events.

Global Events

Global events are called once per build at either the beginning or end of the build process. Any changes made in these events will have a global effect on the entire site.

on_serve

The serve event is only called when the serve command is used during development. It is passed the Server instance which can be modified before it is activated. For example, additional files or directories could be added to the list of "watched" files for auto-reloading.

Parameters:: server: livereload.Server instance; config: global configuration object; builder: a callable which gets passed to each call to server.watch
Returns:: livereload.Server instance

on_config

The config event is the first event called on build and is run immediately after the user configuration is loaded and validated. Any alterations to the config should be made here.

Parameters:: config: global configuration object
Returns:: global configuration object

on_pre_build

The pre_build event does not alter any variables. Use this event to call pre-build scripts.

Parameters:: config: global configuration object

on_files

The files event is called after the files collection is populated from the docs_dir. Use this event to add, remove, or alter files in the collection. Note that Page objects have not yet been associated with the file objects in the collection. Use Page Events to manipulate page specific data.

Parameters:: files: global files collection; config: global configuration object
Returns:: global files collection

on_nav

The nav event is called after the site navigation is created and can be used to alter the site navigation.

Parameters:: nav: global navigation object; config: global configuration object; files: global files collection
Returns:: global navigation object

on_env

The env event is called after the Jinja template environment is created and can be used to alter the Jinja environment.

Parameters:: env: global Jinja environment; config: global configuration object; files: global files collection
Returns:: global Jinja Environment

on_post_build

The post_build event does not alter any variables. Use this event to call post-build scripts.

Parameters:: config: global configuration object

Template Events

Template events are called once for each non-page template. Each template event will be called for each template defined in the extra_templates config setting as well as any static_templates defined in the theme. All template events are called after the env event and before any page events.

on_pre_template

The pre_template event is called immediately after the subject template is loaded and can be used to alter the content of the template.

Parameters:: template: the template contents as string; template_name: string filename of template; config: global configuration object
Returns:: template contents as string

on_template_context

The template_context event is called immediately after the context is created for the subject template and can be used to alter the context for that specific template only.

Parameters:: context: dict of template context variables; template_name: string filename of template; config: global configuration object
Returns:: dict of template context variables

on_post_template

The post_template event is called after the template is rendered, but before it is written to disc and can be used to alter the output of the template. If an empty string is returned, the template is skipped and nothing is is written to disc.

Parameters:: output_content: output of rendered template as string; template_name: string filename of template; config: global configuration object
Returns:: output of rendered template as string

Page Events

Page events are called once for each Markdown page included in the site. All page events are called after the post_template event and before the post_build event.

on_pre_page

The pre_page event is called before any actions are taken on the subject page and can be used to alter the Page instance.

Parameters:: page: elstir.nav.Page instance; config: global configuration object; files: global files collection
Returns:: elstir.nav.Page instance

on_page_read_source

The on_page_read_source event can replace the default mechanism to read the contents of a page's source from the filesystem.

Parameters:: page: elstir.nav.Page instance; config: global configuration object
Returns:: The raw source for a page as unicode string. If None is returned, the default loading from a file will be performed.

on_page_markdown

The page_markdown event is called after the page's markdown is loaded from file and can be used to alter the Markdown source text. The meta- data has been stripped off and is available as page.meta at this point.

Parameters:: markdown: Markdown source text of page as string; page: elstir.nav.Page instance; config: global configuration object; files: global files collection
Returns:: Markdown source text of page as string

on_page_content

The page_content event is called after the Markdown text is rendered to HTML (but before being passed to a template) and can be used to alter the HTML body of the page.

Parameters:: html: HTML rendered from Markdown source as string; page: elstir.nav.Page instance; config: global configuration object; files: global files collection
Returns:: HTML rendered from Markdown source as string

on_page_context

The page_context event is called after the context for a page is created and can be used to alter the context for that specific page only.

Parameters:: context: dict of template context variables; page: elstir.nav.Page instance; config: global configuration object; nav: global navigation object
Returns:: dict of template context variables

on_post_page

The post_page event is called after the template is rendered, but before it is written to disc and can be used to alter the output of the page. If an empty string is returned, the page is skipped and nothing is written to disc.

Parameters:: output: output of rendered template as string; page: elstir.nav.Page instance; config: global configuration object
Returns:: output of rendered template as string

Entry Point

Plugins need to be packaged as Python libraries (distributed on PyPI separate from elstir) and each must register as a Plugin via a setuptools entry_point. Add the following to your setup.py script:

entry_points={
    'elstir.plugins': [
        'pluginname = path.to.some_plugin:SomePluginClass',
    ]
}

The pluginname would be the name used by users (in the config file) and path.to.some_plugin:SomePluginClass would be the importable plugin itself (from path.to.some_plugin import SomePluginClass) where SomePluginClass is a subclass of BasePlugin which defines the plugin behavior. Naturally, multiple Plugin classes could exist in the same module. Simply define each as a separate entry_point.

entry_points={
    'elstir.plugins': [
        'featureA = path.to.my_plugins:PluginA',
        'featureB = path.to.my_plugins:PluginB'
    ]
}

Note that registering a plugin does not activate it. The user still needs to tell elstir to use if via the config.

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elstir Plugins