itertoolset.py


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from itertools import cycle, islice

def roundrobin(*iterables):
    """roundrobin('ABC', 'D', 'EF') --> A D E B F C"""
    pending = len(iterables)
    nexts = cycle(iter(it).next for it in iterables)
    while pending:
        try:
            for next in nexts:
                yield next()
        except StopIteration:
            pending -= 1
            nexts = cycle(islice(nexts, pending))