python – Pythonic way to combine two lists in an alternating fashion?

python – Pythonic way to combine two lists in an alternating fashion?

Heres one way to do it by slicing:

>>> list1 = [f, o, o]
>>> list2 = [hello, world]
>>> result = [None]*(len(list1)+len(list2))
>>> result[::2] = list1
>>> result[1::2] = list2
>>> result
[f, hello, o, world, o]

Theres a recipe for this in the itertools documentation:

from itertools import cycle, islice

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))

EDIT:

For pythons version greater than 3:

from itertools import cycle, islice

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))

python – Pythonic way to combine two lists in an alternating fashion?

import itertools
print [x for x in itertools.chain.from_iterable(itertools.izip_longest(list1,list2)) if x]

I think this is the most pythonic way of doing it.