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Introduction to plugins

What are plugins?

A plugin is a Python package that encapsulates a set of functionality designed to be used in more than one application. It can define database models, actors, actions, fixtures, template files, JavaScript snippets, dependencies, and configuration settings. None of these are mandatory.

A plugin in Lino corresponds to what Django calls an “application” (more about this controversial topic in What is an application?).

See Plugins reference for developers for a list of the plugins defined in Lino and the XL.

Usage overview

As an application developer you define which plugins to use by writing a get_installed_plugins method for your Site.

The plugin developer defines a plugin in the __init__.py file of the package. Lino expects this file to define a class named Plugin, which inherits from the abstract base Plugin class. Your Plugin class is the central description of your plugin.

Here is a fictive example:

from lino.api import ad, _

class Plugin(ad.Plugin):
    verbose_name = _("Better calendar")
    extends = 'mylib.cal'
    needs_plugins  = ['lino_xl.lib.contacts']

    def setup_main_menu(self, site, user_type, m):
        m = m.add_menu(self.app_label, self.verbose_name)
        m.add_action('cal.Teams')
        m.add_action('cal.Agendas')

A plugin can depend on other plugins by specifying them in the needs_plugins attribute. This means that when you install this plugin, Lino will automatically install these other plugins as well

A plugin can define a set of menu commands using methods like setup_main_menu. This is explained in More about the application menu.

A plugin can extend another plugin by inheriting from its Plugin class. This is explained in Plugin inheritance.

A plugin that extends another plugin can optionally extend one or multiple database models defined by the parent plugin. If it does so, it must declare their names in extends_models.