code: def by_image_seq(blocks, image_seq):
      
      return list(filter(lambda block: blocks[block].ec_hdr.image_seq == image_seq, blocks))
docs: Filter blocks to return only those associated with the provided image_seq number.
  
      Argument:
      List:blocks       -- List of block objects to sort.
      Int:image_seq    -- image_seq number found in ec_hdr.
      
      Returns:
      List        -- List of block indexes matching image_seq number.