WC_Product_Attribute::is_taxonomy PHP Method

    public function is_taxonomy()
    {
        return 0 < $this->get_id();
    }

 /**
  * Add an attribute row.
  */
 public static function add_attribute()
 {
     ob_start();
     check_ajax_referer('add-attribute', 'security');
     if (!current_user_can('edit_products')) {
         die(-1);
     }
     $i = absint($_POST['i']);
     $metabox_class = array();
     $attribute = new WC_Product_Attribute();
     $attribute->set_id(wc_attribute_taxonomy_id_by_name(sanitize_text_field($_POST['taxonomy'])));
     $attribute->set_name(sanitize_text_field($_POST['taxonomy']));
     $attribute->set_visible(apply_filters('woocommerce_attribute_default_visibility', 1));
     $attribute->set_variation(apply_filters('woocommerce_attribute_default_is_variation', 0));
     if ($attribute->is_taxonomy()) {
         $metabox_class[] = 'taxonomy';
         $metabox_class[] = $attribute->get_name();
     }
     include 'admin/meta-boxes/views/html-product-attribute.php';
     die;
 }