WP - Only return posts in search

search-filter.php

/**
 * Search should only return posts
 */
function search_filter($query) {
    if (!$query->is_admin && $query->is_search) {
      $query->set('post_type', 'post');
      // $query->set('post__not_in', array(1,5,10));
    }
    return $query;
  }
}
add_filter('pre_get_posts', 'search_filter');