The Air can do a lot. The CPU is a couple of generations behind now, but that's not a big problem. It's still the cheapest way to get a portable Mac, and for that reason it will be worth a consideration. It all works well, it just seems old compared to the newer macs. The screen is 2010 technology, it's not really that thin anymore relatively and the computer is kinda wide with large bezels... but it's still a really capable computer.
Likewise the 2015 15" is a good buy if you need the power, screen size and the ports.
It can do coding just fine. I'd get the 15" only if I was going to work on compiling really huge projects, or I was doing stuff that I would end up waiting on the computer a lot. Exporting video, doing really heavy scientific calculations...
I use a 2015 Air for pretty large Logic Pro X projects and it manages just fine.