code: def _get_contigs_to_keep(self, filename):
          '''Returns a set of names from file called filename. If filename is None, returns an empty set'''
          if filename is None:
              return set()
  
          with open(filename) as f:
              return {line.rstrip() for line in ff _get_contigs_to_keep(self, filename):
          '''Returns a set of names from file called filename. If filename is None, returns an empty set'''
          if filename is None:
              return set()
  
          with open(filename) as f:
              return {line.rstrip() for line in f}
docs: Returns a set of names from file called filename. If filename is None, returns an empty set