Rolling or sliding window iterator?

Question

I need a rolling window (aka sliding window) iterable over a sequence/iterator/generator. Default Python iteration can be considered a special case, where the window length

Answer 1

Multiple iterators!

def window(seq, size, step=1):
    # initialize iterators
    iters = [iter(seq) for i in range(size)]
    # stagger iterators (without yielding)
    [next(iters[i]) for j in range(size) for i in range(-1, -j-1, -1)]
    while(True):
        yield [next(i) for i in iters]
        # next line does nothing for step = 1 (skips iterations for step > 1)
        [next(i) for i in iters for j in range(step-1)]

next(it) raises StopIteration when the sequence is finished, and for some cool reason that's beyond me, the yield statement here excepts it and the function returns, ignoring the leftover values that don't form a full window.

Anyway, this is the least-lines solution yet whose only requirement is that seq implement either __iter__ or __getitem__ and doesn't rely on itertools or collections besides @dansalmo's solution :)