I get a weird error while trying to retrieve a single project commit. It turns out that the data I'm passing in is actually of the "unicode" type and not a string. I think you need a little better handling for unicode strings. This change on line 526 fixed the issue for me:

-        if data is None or isinstance(data, int) or isinstance(data, str):
+        if data is None or isinstance(data, int) or isinstance(data, str) or isinstance(data, unicode):

Not sure if there is a more general solution for this. I also was able to fix it once I tracked it down by converting my id data to a string before passing it to the API.