def METHOD_NAME(self, blob):
    res, msg = TransactionSetCore.METHOD_NAME(self, blob)
    # generate backwards compatibly broken exceptions
    if res == rpm.RPMRC_NOKEY:
        raise rpm.error("public key not available")
    elif res == rpm.RPMRC_NOTTRUSTED:
        raise rpm.error("public key not trusted")
    elif res != rpm.RPMRC_OK:
        raise rpm.error(msg)