If you want to check out my latest version, here's the repo:
https://gitlab.com/anthem/py-threedub
This supports printing, getting the raw or a (slightly) translated status from the Jr, and a couple more small things. There's nothing very useful other than those operations that can be done with the Jr (that I know of -- there may be hidden secrets I'm not aware of).
This code implements firmware update, too. Feel free to play with it, but you'll have to reenable it in printers.py yourself as I've disabled it for safety reasons. However I believe the file upload process to be safe, there are just certain times and ways that you shouldn't use it. In my case, I may have used a bad firmware file, or my attempt to update while printing could have been what blew up my firmware. I'm just not sure. Unfortunately because the firmware decryption happens on-board and no one has cracked the firmware encryption yet, there's currently no way to restore stock firmware (and no, there's still no repetier support for the board).
Be aware that the serial communications can be a little tricky. I've sometimes had to retry printing several times before it succeeds. Usually that looks like a long pause in the upload progress followed by an error message. I think it has something to do with timing issues buffering the serial data one way or the other, as it seems to happen more on slower systems like my Raspberry Pi I set up as a print server. That said, the protocol is in place and if anyone can improve on the situation they're welcome to do so. I probably won't be spending much more time on it because my Jr is soon to be a RAMPSenstein.