code: def fetch(self, is_dl_forced=False):
          
  
          file_paths = self._get_file_paths(self.tax_ids, 'protein_links')
          self.get_files(is_dl_forced, file_paths)
          self.get_files(is_dl_forced, self.id_map_files)
docs: Override Source.fetch()
          Fetches resources from String
  
          We also fetch ensembl to determine if protein pairs are from
          the same species
          Args:
              :param is_dl_forced (bool): Force download
          Returns:
              :return None