A beets plugin is just a Python module inside the beetsplug namespace package. (Check out this Stack Overflow question about namespace packages if you haven’t heard of them.) So, to make one, create a directory called beetsplug and put two files in it: one called __init__.py and one called myawesomeplugin.py (but don’t actually call it that). Your directory structure should look like this:
beetsplug/
__init__.py
myawesomeplugin.py
Then, you’ll need to put this stuff in __init__.py to make beetsplug a namespace package:
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
That’s all for __init__.py; you can can leave it alone. The meat of your plugin goes in myawesomeplugin.py. There, you’ll have to import the beets.plugins module and define a subclass of the BeetsPlugin class found therein. Here’s a skeleton of a plugin file:
from beets.plugins import BeetsPlugin
class MyPlugin(BeetsPlugin):
pass
Once you have your BeetsPlugin subclass, there’s a variety of things your plugin can do. (Read on!)
To use your new plugin, make sure your beetsplug directory is in the Python path (using PYTHONPATH or by installing in a virtualenv, for example). Then, as described above, edit your .beetsconfig to include plugins=myawesomeplugin (substituting the name of the Python module containing your plugin).
Plugins can add new subcommands to the beet command-line interface. Define the plugin class’ commands() method to return a list of Subcommand objects. (The Subcommand class is defined in the beets.ui module.) Here’s an example plugin that adds a simple command:
from beets.plugins import BeetsPlugin
from beets.ui import Subcommand
my_super_command = Subcommand('super', help='do something super')
def say_hi(lib, config, opts, args):
print "Hello everybody! I'm a plugin!"
my_super_command.func = say_hi
class SuperPlug(BeetsPlugin):
def commands(self):
return [my_super_command]
To make a subcommand, invoke the constructor like so: Subcommand(name, parser, help, aliases). The name parameter is the only required one and should just be the name of your command. parser can be an OptionParser instance, but it defaults to an empty parser (you can extend it later). help is a description of your command, and aliases is a list of shorthand versions of your command name.
You’ll need to add a function to your command by saying mycommand.func = myfunction. This function should take the following parameters: lib (a beets Library object), config (a ConfigParser object containing the configuration values), and opts and args (command-line options and arguments as returned by OptionParser.parse_args).
The function should use any of the utility functions defined in beets.ui. Try running pydoc beets.ui to see what’s available.
You can add command-line options to your new command using the parser member of the Subcommand class, which is an OptionParser instance. Just use it like you would a normal OptionParser in an independent script.
Event handlers allow plugins to run code whenever something happens in beets’ operation. For instance, a plugin could write a log message every time an album is successfully autotagged or update MPD’s index whenever the database is changed.
You can “listen” for events using the BeetsPlugin.listen decorator. Here’s an example:
from beets.plugins import BeetsPlugin
class SomePlugin(BeetsPlugin):
pass
@SomePlugin.listen('pluginload')
def loaded():
print 'Plugin loaded!'
Pass the name of the event in question to the listen decorator. The events currently available are:
The included mpdupdate plugin provides an example use case for event listeners.
Plugins in can also enhance the functionality of the autotagger. For a comprehensive example, try looking at the chroma plugin, which is included with beets.
A plugin can extend three parts of the autotagger’s process: the track distance function, the album distance function, and the initial MusicBrainz search. The distance functions determine how “good” a match is at the track and album levels; the initial search controls which candidates are presented to the matching algorithm. Plugins implement these extensions by implementing three methods on the plugin class:
When implementing these functions, it will probably be very necessary to use the functions from the beets.autotag and beets.autotag.mb modules, both of which have somewhat helpful docstrings.
Plugins can configure themselves using the .beetsconfig file. Define a configure method on your plugin that takes an OptionParser object as an argument. Then use the beets.ui.config_val convenience function to access values from the config file. Like so:
class MyPlugin(BeetsPlugin):
def configure(self, config):
number_of_goats = beets.ui.config_val(config, 'myplug', 'goats', '42')
Try looking at the mpdupdate plugin (included with beets) for an example of real-world use of this API.
Beets supports function calls in its path format syntax (see Path Formats). Beets includes a few built-in functions, but plugins can add new functions using the template_func decorator. To use it, decorate a function with MyPlugin.template_func("name") where name is the name of the function as it should appear in template strings.
Here’s an example:
class MyPlugin(BeetsPlugin):
pass
@MyPlugin.template_func('initial')
def _tmpl_initial(text):
if text:
return text[0].upper()
else:
return u''
This plugin provides a function %initial to path templates where %initial{$artist} expands to the artist’s initial (its capitalized first character).
Plugins can also add template fields, which are computed values referenced as $name in templates. To add a new field, decorate a function taking a single parameter, item, with MyPlugin.template_field("name"). Here’s an example that adds a $disc_and_track field:
@MyPlugin.template_field('disc_and_track')
def _tmpl_disc_and_track(item):
"""Expand to the disc number and track number if this is a
multi-disc release. Otherwise, just exapnds to the track
number.
"""
if item.disctotal > 1:
return u'%02i.%02i' % (item.disc, item.track)
else:
return u'%02i' % (item.track)
With this plugin enabled, templates can reference $disc_and_track as they can any standard metadata field.
MediaFile is the file tag abstraction layer that beets uses to make cross-format metadata manipulation simple. Plugins can add fields to MediaFile to extend the kinds of metadata that they can easily manage.
The item_fields method on plugins should be overridden to return a dictionary whose keys are field names and whose values are descriptor objects that provide the field in question. The descriptors should probably be MediaField instances (defined in beets.mediafile). Here’s an example plugin that provides a meaningless new field “foo”:
from beets import mediafile, plugins, ui
class FooPlugin(plugins.BeetsPlugin):
def item_fields(self):
return {
'foo': mediafile.MediaField(
mp3 = mediafile.StorageStyle(
'TXXX', id3_desc=u'Foo Field'),
mp4 = mediafile.StorageStyle(
'----:com.apple.iTunes:Foo Field'),
etc = mediafile.StorageStyle('FOO FIELD')
),
}
Later, the plugin can manipulate this new field by saying something like mf.foo = 'bar' where mf is a MediaFile instance.
Note that, currently, these additional fields are only applied to MediaFile itself. The beets library database schema and the Item class are not extended, so the fields are second-class citizens. This may change eventually.