code: def make_index(gff_file):
      
      import gffutils
      db_file = gff_file + ".db"
  
      if need_update(gff_file, db_file):
          if op.exists(db_file):
              os.remove(db_file)
          logging.debug("Indexing `{0}`".format(gff_file))
          gffutils.create_db(gff_file, db_file, merge_strategy="create_unique")
      else:
          logging.debug("Load index `{0}`".format(gff_file))
  
      return gffutils.FeatureDB(db_file)
docs: Make a sqlite database for fast retrieval of features.