The
Cosina 55mm f/1.2 is K-mount, but not "A". It's fully manual.
And there are no half-stop settings on the aperture ring. In fact, it's a little worse than that -- it goes from 1.2 to 2.0, then 2.8, 4, etc. So the first interval is like 1 1/3 stops. You can sorta balance it between clicks, but that's hardly reliable and certainly not accurately repeatable.
But hey, it's a great lens. I own it and love it. It's not that hard to meter with (love that green button!). And it can be had for $200 or sometimes even a bit less. I got mine on eBay for $168, but had to deal with bent and banged-up filter threads.
It's a great way to get your feet wet without spending too much. If you like it, you can probably resell it for about what you paid, and upgrade to an A 1.2 once you track one down. Or maybe you'll like the Cosina enough to keep it. I do!