> Also it would be nice to clarify if struct.Struct.format is meant to be > a byte string.

Hmm.  That seems wrong to me.  After all, the format string is supposed to be a piece of human-readable text rather than a collection of bytes.  I think it's borderline acceptable to allow a bytes instance to be passed in for the format (practicality beats purity and all that), but I'd say that the output format should definitely be unicode.