Limit searches to a specific custom post type

cpt_limit_search.php

function sw_cpt_search($query) {


    if (
        isset ( $_REQUEST['search'] ) &&
        $_REQUEST['search'] == 'landlord' &&
        ! is_admin() &&
        $query -> is_search &&
        $query -> is_main_query()
    ) {

		// limit the query to 'landlord' posts
        $query->set('post_type', 'landlords');


}
add_filter('pre_get_posts', 'sw_cpt_search');