Yea, fortunately pythonpy supports lazy iteration over sys.stdin when you really need it. Just like in python, the syntax won't be as nice as using a list. But it works:

  py 'itertools.count(1)' | py 'itertools.islice(stdin, 0, 10, 2)'

However, the number of times that you need this are surprisingly rare. Most lazy operations don't require that each row be aware of the surrounding row context, and using the much simpler:

  py -x 'new_row_from_old_row(x)'

will get the job done in a lazy fashion. Usually, when you need rows to be context aware, as in:

  py -l 'sorted(l)'

or

  py -l 'set(l)'

it's just not possible to accomplish your task without reading in all of stdin.