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

a slightly modified version of the deque window, to make it a true rolling window. So that it starts being populated with just one element, then grows to it's maximum window size, and then shrinks as it's left edge comes near the end:

from collections import deque
def window(seq, n=2):
    it = iter(seq)
    win = deque((next(it, None) for _ in xrange(1)), maxlen=n)
    yield win
    append = win.append
    for e in it:
        append(e)
        yield win
    for _ in xrange(len(win)-1):
        win.popleft()
        yield win

for wnd in window(range(5), n=3):
    print(list(wnd))

this gives

[0]
[0, 1]
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
[3, 4]
[4]