I'm developing a new frontend for yt <https://bitbucket.org/eschnett/yt>. I am currently encountering this error <http://pastebin.com/EYauU1rv>.

I don't know what causes this error. The error message mentions an __init__ function, but I don't know which __init__ function this is, nor whether the problem is in the caller or the callee. I'd be grateful for any feedback.

-erik