`nbest_list_item.ptb_parse` is an `InputTree` object (wrapped SWIG object -- see https://github.com/BLLIP/bllip-parser/blob/master/first-stage/PARSE/swig/wrapper.i#L347 and https://github.com/BLLIP/bllip-parser/blob/master/first-stage/PARSE/InputTree.h). I'm don't think BLLIP Parser supports Unicode internally properly and a quick test indicates that it doesn't. What does this mean for NLTK wrapping? Would it be okay to have it raise an error if asked to parse non-ASCII text?