Add Path Format Functions and Fields

Beets supports function calls in its path format syntax (see Path Formats). Beets includes a few built-in functions, but plugins can register new functions by adding them to the template_funcs dictionary.

Here's an example:

class MyPlugin(BeetsPlugin):
    def __init__(self):
        super().__init__()
        self.template_funcs["initial"] = _tmpl_initial


def _tmpl_initial(text: str) -> str:
    if text:
        return text[0].upper()
    else:
        return ""

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, add a function that takes an Item object to the template_fields dictionary on the plugin object. Here's an example that adds a $disc_and_track field:

class MyPlugin(BeetsPlugin):
    def __init__(self):
        super().__init__()
        self.template_fields["disc_and_track"] = _tmpl_disc_and_track


def _tmpl_disc_and_track(item: Item) -> str:
    """Expand to the disc number and track number if this is a
    multi-disc release. Otherwise, just expands to the track
    number.
    """
    if item.disctotal > 1:
        return "%02i.%02i" % (item.disc, item.track)
    else:
        return "%02i" % (item.track)

With this plugin enabled, templates can reference $disc_and_track as they can any standard metadata field.

This field works for item templates. Similarly, you can register album template fields by adding a function accepting an Album argument to the album_template_fields dict.