Wordpress | Post per page for Custom post types

/* Set posts per page for a custom post type in wordpress.php */
function set_posts_per_page_for_towns_cpt( $query ) {
  if ( !is_admin() && $query->is_main_query() && is_post_type_archive( 'towns' ) ) {
    $query->set( 'posts_per_page', '10' );
  }
}
add_action( 'pre_get_posts', 'set_posts_per_page_for_towns_cpt' );