The inline plugin lets you use Python expressions to customize your path formats. Using it, you can define template fields in your beets configuration file and refer to them from your template strings in the [paths] section (see .beetsconfig).
To use inline field definitions, first enable the plugin by putting inline on your plugins line, like so:
[beets]
plugins: inline
Then, make a [pathfields] section in your config file. In this section, every line defines a new template field; the key is the name of the field (you’ll use the name to refer to the field in your templates) and the value is a Python expression. The expression has all of a track’s fields in scope, so you can refer to any normal attributes (such as artist or title) as Python variables. Here are a couple of examples:
[pathfields]
artist_initial: artist[0].upper() + u'.'
disc_and_track: u'%02i.%02i' % (disc, track) if
disctotal > 1 else u'%02i' % (track)
(Note that the config file’s syntax allows newlines in values if the subsequent lines are indented.) These examples define $artist_initial and $disc_and_track fields that can be referenced in path templates like so:
[paths]
default: $artist_initial/$artist/$album/$disc_and_track $title