Beet-MusicBrainz-Collection is a project mainly written in Python, it's free.
Use beets to update your MusicBrainz collection
This is a plugin for beets that will add the command mbupdate to beets, which will update your collection on MusicBrainz.
You will need to add the following to your beets configuration file:
[musicbrainz]
user: yourusername
pass: yourpassword