code: def fetch(self, is_dl_forced=False):
          
          self.get_files(is_dl_forced)
  
          # load and tag a list of OMIM IDs with types
          self.omim_type = self.find_omim_type()
  
          return
docs: We fetch GeneReviews id-label map and id-omim mapping files from NCBI.
          :return: None