groupn.py

from itertools import groupby, count


def debug_iter(iter):
    for x in iter:
        print "=> %d" % x
        yield x


def groupn(n, it):
    c = count()
    return ((g, sit) for g, sit in groupby(it, key=lambda x: c.next() // n))


for g, sit in groupn(5, debug_iter(xrange(20))):
    for s in sit:
        print g, s