How to approach teachnig programming for people with ADHD?

I'm helping out a guy with ADHD learn Python, and he's struggling a lot. This has mainly to do with the high-level program structure, and the concept that variables aren't constant, but only constrained by their type. While he's able to nearly ace tests, he takes hours to implement relatively easy functions. He can implement individual statements or reason about principles quite well, but connecting different functions (or even two lines of code) is super difficult (e.g. when he has to group a list by some attribute).

I suspect that he's unable to mentally place the different elements of an algorithm/program in his mind and then refer to them. I tried explaining how he should structure different components many times (by examples, theory, visually, code rundowns), but it's really slow. Can you recommend any method/approach to help him learn the basics?