code: def get_shred_id(id):
      
      try:
          parts = id.split(".")
          aid = ".".join(parts[:2])
          fid = int(parts[2].replace("frag", ""))
      except:
          aid, fid = None, None
      return aid, fid
docs: >>> get_shred_id("ca-bacs.5638.frag11.22000-23608")
      ("ca-bacs.5638", 11)