variable filter-list item

I actually find a block in a drawing with :

(setq ss (ssget "_X" '((2 . "blockname"))))

But I want the blockname to be a variable.

So I want to do :
(setq a "blockname") and then
(setq ss (ssget "_X" '((2 . a)))).
But this do not work. I tries : (list a), (setq a) but that doesn't work either
thanks

Because you are using single-quote (') your A symbol is not being evaluated.

Try using back-quote instead:

(setq ss (ssget "_X" `((2 . ,a)))).

A version without backquote would look like:

(setq ss (ssget "_X" (list (cons 2 a))))

Thanks Edgar, that work