The roundrobin example in the Recipes section of the itertools documentation (http://docs.python.org/3/library/itertools.html#itertools-recipes) is overly complex. Here is a more straightforward implementation:

def roundrobin(*iterables):
    "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    sentinel = object()
    it = chain.from_iterable(zip_longest(fillvalue=sentinel, *iterables))
    return (i for i in it if i is not sentinel)

Not only is it one-third the lines of the existing example, benchmarks show it to be more than twice as fast.

See attached patch file.