Beets: Extendable command-line tool & library for cataloging, manipulating, & accessing your music library written in Python

http://beets.radbox.org/

Example:

$ beet import ~/music/ladytron
Tagging:
    Ladytron - Witching Hour
(Similarity: 98.4%)
 * Last One Standing      -> The Last One Standing
 * Beauty                 -> Beauty*2
 * White Light Generation -> Whitelightgenerator
 * All the Way            -> All the Way...

From the Beets Github page

• Fetch or calculate all the metadata you could possibly need: album art, lyrics,
  genres, tempos, ReplayGain levels, or acoustic fingerprints.
• Get metadata from MusicBrainz, Discogs, or Beatport. Or guess metadata using
  songs’ filenames or their acoustic fingerprints.
• Transcode audio to any format you like.
• Check your library for duplicate tracks and albums or for albums that are missing tracks.
• Clean up crufty tags left behind by other, less-awesome tools.
• Embed and extract album art from files’ metadata.
• Browse your music library graphically through a Web browser and play it in
  any browser that supports HTML5 Audio.
• Analyze music files’ metadata from the command line.
• Listen to your library with a music player that speaks the MPD protocol and
  works with a staggering variety of interfaces.
• If beets doesn’t do what you want yet, writing your own plugin is shockingly
  simple if you know a little Python.