@blueprint.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

bp = Blueprint('errors', __name__)

@bp.app_errorhandler(404)
def handle_404(err):
    return render_template('404.html'), 404

@bp.app_errorhandler(500)
def handle_500(err):
    return render_template('500.html'), 500