code: def copy_selected_sources(cls, roi, source_names):
          
          roi_new = cls.make_roi()
          for source_name in source_names:
              try:
                  src_cp = roi.copy_source(source_name)
              except Exception:
                  continue
              roi_new.load_source(src_cp, build_index=False)
          return roi_new
docs: Build and return a `fermipy.roi_model.ROIModel` object
          by copying selected sources from another such object