def src_file(self):
        """
        Get the latest src_uri for a stage 3 tarball.

        Returns (str):
            Latest src_uri from gentoo's distfiles mirror.
        """
        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
Get the latest src_uri for a stage 3 tarball.

        Returns (str):
            Latest src_uri from gentoo's distfiles mirror.