def __filter_assets(catalogs, attachments):
    """
    Separate series from episode assets.

    :param catalogs: All catalogs
    :type: list
    :param attachments: All attachments
    :type attachments: list
    :return: Episode catalogs, episode attachments, series catalogs, series attachments
    :rtype: list, list, list, list
    """
    series_catalogs = [catalog for catalog in catalogs if "series" in catalog.flavor]
    episode_catalogs = [catalog for catalog in catalogs if catalog not in series_catalogs]

    series_attachments = [attachment for attachment in attachments if "series" in attachment.flavor]
    episode_attachments = [attachment for attachment in attachments if attachment not in series_attachments]

    return episode_catalogs, episode_attachments, series_catalogs, series_attachments