user (Required) : The user name to fetch top artists for. period (Optional) : overall | 7day | 1month | 3month | 6month | 12month - The time period over which to retrieve top artists for. limit (Optional) : The number of results to fetch per page. Defaults to 50. page (Optional) : The page number to fetch. Defaults to first page. api_key (Required) : A Last.fm API key.