A party may take an appeal within the space of twenty days after the date of the judgment of which he complains, during which period of twenty days extract shall not be competent; but on the expiration of the foresaid period, if no appeal shall have been taken, the clerk of the court may give out the extract; it being competent, however, to take such appeal at any time within the period of six months from the date of final judgment in the cause, unless the judgment has previously been extracted or implemented.