interleaving 2 lists of unequal lengths [duplicate]

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You can use itertools.izip_longest here:

>>> from itertools import izip_longest
>>> xs = [1,2,3]
>>> ys = ["hi","bye","no","yes","why"]
>>> s = object()
>>> [y for x in izip_longest(xs, ys, fillvalue=s) for y in x if y is not s]
[1, 'hi', 2, 'bye', 3, 'no', 'yes', 'why']

Using roundrobin recipe from itertools, no sentinel value required here:

from itertools import *
def roundrobin(*iterables):
    "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    # Recipe credited to George Sakkis
    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))

Demo:

>>> list(roundrobin(xs, ys))
[1, 'hi', 2, 'bye', 3, 'no', 'yes', 'why']
>>> list(roundrobin(ys, xs))
['hi', 1, 'bye', 2, 'no', 3, 'yes', 'why']

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