[issue32099] Use range in itertools roundrobin recipe

[Serhiy Storchaka]

Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:

Today I have published a similar recipe on Python-Ideas. It uses popleft/append instead of __getitem__/rotate.

def roundrobin(*iterables):
    "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    nexts = deque(iter(it).__next__ for it in iterables)
    popleft = nexts.popleft
    append = nexts.append
    while nexts:
        next = popleft()
        try:
            yield next()
        except StopIteration:
            pass
        else:
            append(next)

It is faster (10-25%) in all microbenchmarks that I did (Steven's benchmarks for small number of iterables and my examples for large number of iterables).

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<https://bugs.python.org/issue32099>
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