code: def src_file(self):
          
          try:
              src_uri = (curl[Gentoo._LATEST_TXT] | tail["-n", "+3"]
                         | cut["-f1", "-d "])().strip()
          except ProcessExecutionError as proc_ex:
              src_uri = "NOT-FOUND"
              LOG.error("Could not determine latest stage3 src uri: %s",
                        str(proc_ex))
          return src_uri
docs: Get the latest src_uri for a stage 3 tarball.
  
          Returns (str):
              Latest src_uri from gentoo's distfiles mirror.