Get a champion mastery by player ID and champion ID.

        :param string                           region: the region to execute this request on
        :param string encrypted_summoner_id:    Summoner ID associated with the player
        :param long champion_id:                Champion ID to retrieve Champion Mastery for

        :returns: ChampionMasteryDTO: This object contains single Champion Mastery information for
                                      player and champion combination.

def by_summoner_by_champion(self, region, encrypted_summoner_id, champion_id):
        """
        Get a champion mastery by player ID and champion ID.

        :param string                           region: the region to execute this request on
        :param string encrypted_summoner_id:    Summoner ID associated with the player
        :param long champion_id:                Champion ID to retrieve Champion Mastery for

        :returns: ChampionMasteryDTO: This object contains single Champion Mastery information for
                                      player and champion combination.
        """
        url, query = ChampionMasteryApiV4Urls.by_summoner_by_champion(
            region=region,
            encrypted_summoner_id=encrypted_summoner_id,
            champion_id=champion_id,
        )
        return self._raw_request(
            self.by_summoner_by_champion.__name__, region, url, query
        )