tokens: This is really important if you 're doing things like file IO to map your values ( e.g . if your values are filenames and you 're mapping to their contents ) and you do n't want to read the file over and over again .
ner_tags: O O O O O O O O O O O O O B-Data_Structure O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O