code: def update(self, dicomset):
          
          if not isinstance(dicomset, DicomFileSet):
              raise ValueError('Given dicomset is not a DicomFileSet.')
  
          self.items = list(set(self.items).update(dicomset))
docs: Update this set with the union of itself and dicomset.
  
          Parameters
          ----------
          dicomset: DicomFileSet