code: def finalize(self):
          
          # Merge all the out_DDB files found in work.outdir.
          ddb_files = list(filter(None, [work.outdir.has_abiext("DDB") for work in self]))
  
          # Final DDB file will be produced in the outdir of the work.
          out_ddb = self.outdir.path_in("out_DDB")
          desc = "DDB file merged by %s on %s" % (self.__class__.__name__, time.asctime())
  
          mrgddb = wrappers.Mrgddb(manager=self.manager, verbose=0)
          mrgddb.merge(self.outdir.path, ddb_files, out_ddb=out_ddb, description=desc)
          print("Final DDB file available at %s" % out_ddb)
  
          # Call the method of the super class.
          retcode = super().finalize()
          return retcode
docs: This method is called when the flow is completed.