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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _extract_links_from_lecture_assets(self, asset_ids):
 """ Extract links to files of the asset ids. @param asset_ids: List of asset ids. @type asset_ids: [str] @return: @see CourseraOnDemand._extract_links_from_text """

        links = {}

        def _add_asset(name, url, destination):
            filename, extension = os.path.splitext(clean_url(name))
            if extension is '':
                return

            extension = clean_filename(
                extension.lower().strip('.').strip(),
                self._unrestricted_filenames)
            basename = clean_filename(
                os.path.basename(filename),
                self._unrestricted_filenames)
            url = url.strip()

            if extension not in destination:
                destination[extension] = []
            destination[extension].append((url, basename))

        for asset_id in asset_ids:
            for asset in self._get_asset_urls(asset_id):
                _add_asset(asset['name'], asset['url'], links)

        return links