def request_playlist_videos(youtube, playlist_id, num_results, page_token=None):
    """Request all the videos from a playlist_id using YouTube's api."""
    if page_token:
        request = youtube.playlistItems().list(
            part="snippet",
            maxResults=num_results,
            playlistId=playlist_id,
            pageToken=page_token
        )
    else:
        request = youtube.playlistItems().list(
                part="snippet",
                maxResults=num_results,
                playlistId=playlist_id,
            )
    response = request.execute()
    return response