code: def itertrajs(meta, stride=1):
      
  
      tops = preload_tops(meta)
      for i, row in meta.iterrows():
          yield i, md.join(md.iterload(row['traj_fn'],
                                       top=tops[row['top_fn']],
                                       stride=stride),
                           discard_overlapping_frames=False,
                           check_topology=False)
docs: Load one mdtraj trajectory at a time and yield it.
  
      MDTraj does striding badly. It reads in the whole trajectory and
      then performs a stride. We join(iterload) to conserve memory.