def _getNextArticleBatch(self):
        """download next batch of events based on the event uris in the uri list"""
        eventUri = self.queryParams["eventUri"]
        # move to the next page to download
        self._articlePage += 1
        # if we have already obtained all pages, then exit
        if self._totalPages != None and self._articlePage > self._totalPages:
            return
        if self._er._verboseOutput:
            print("Downloading article page %d from event %s" % (self._articlePage, eventUri))

        self.setRequestedResult(RequestEventArticles(
            page = self._articlePage,
            sortBy = self._articlesSortBy, sortByAsc = self._articlesSortByAsc,
            returnInfo = self._returnInfo,
            **self.queryParams))
        res = self._er.execQuery(self)
        if "error" in res:
            print(res["error"])
        else:
            self._totalPages = res.get(eventUri, {}).get("articles", {}).get("pages", 0)
        arts = res.get(eventUri, {}).get("articles", {}).get("results", [])
        self._articleList.extend(arts)
download next batch of events based on the event uris in the uri list