RPython and PyPy are (IMO) the coolest Python projects out there. I made a little Brainfuck intepreter with it and it was super simple, but making small changes

RPython and PyPy are (IMO) the coolest Python projects out there. I made a little Brainfuck intepreter with it and it was super simple, but making small changes seemed to slow it down a lot. There is very little visibility as to how the code is compiled - i.e should I use a list or a tuple for some things? Can PyPy work out that a list is fixed sized? How should I classes to make them as efficient as possible (like are classes with two or so fields passed as structs)?