label on the left side of minted or listings

Hi there,
Hi there,
I am typesetting code using minted or listings package. It works fine. Now I am hoping to add a label, similar to equation label, on the left side of the code block, looks like following. (%o1) is the label.
(%o1)  code here here here
        code here here
        code here
        code
However, I can't find a way to do this. Any hint will be appreciated.
Best wishes,
Jinsong