Question

I have two lists:
[a, b, c] [d, e, f]
I want:
[a, d, b, e, c, f]

What’s a simple way to do this in Python?

Answer 1

One option is to use a combination of chain.from_iterable() and zip():

# Python 3:
from itertools import chain
list(chain.from_iterable(zip(list_a, list_b)))

# Python 2:
from itertools import chain, izip
list(chain.from_iterable(izip(list_a, list_b)))

Edit: As pointed out by sr2222 in the comments, this does not work
well if the lists have different lengths. In that case, depending on
the desired semantics, you might want to use the (far more general) roundrobin()
function from the recipe
section of the
itertools documentation:

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))