def channel_video_success(row, weights=None):
    """Get sum of z-scores as a success metric."""
    metric_cols = ["z_comments", "z_dislikes",
                   "z_likes", "z_views"]
    if weights is None:
        weights = [1 for _ in metric_cols]
    
    scores = [row[key] for key in metric_cols]
    return sum(scores)