Python: Intertwining two lists

Question

What is the pythonic way of doing the following:

I have two lists a and b of the same length n, and I want to form the list

c = [a[0], b[0], a[1], b[1], ..., a[n-1], b[n-1]]

Answer 1

c = [item for pair in zip(a, b) for item in pair]

Read documentation about zip.

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For comparison with Ignacio's answer see this question: How do I convert a tuple of tuples to a one-dimensional list using list comprehension?

Answer 2

c = list(itertools.chain.from_iterable(itertools.izip(a, b)))

Answer 3

c = [item for t in zip(a,b) for item in t]

Answer 4

c = [item for i in zip(a,b) for item in i]

Alternatively you could try:

c=[(a,b)[i%2][i/2] for i in xrange(2*n)]

which is of course less readable

Answer 5

Here is another way:

sum(([x,y] for (x,y) in zip(a,b)), [])

(Maybe not very efficient since you form both temporary tuples (x,y) and temporary lists [x,y].)

Answer 6

How about this one (tested on Python 2 and 3):

list(sum(zip(a, b), ()))

or in numpy:

import numpy as np
np.vstack((a, b)).T.flatten().tolist()