Question

I have a list consisting of other lists and some zeroes, for example:

x = [[1, 1, 2], [1, 1, 1, 2], [1, 1, 2], 0, 0, 0]

I would like to generate all the combinations of this list while keeping the order of the inner lists unchanged, so

[[1, 1, 2], 0, 0, [1, 1, 1, 2], [1, 1, 2], 0]

is fine, but

[[1, 1, 1, 2], [1, 1, 2], 0, 0, [1, 1, 2], 0]

isn’t. I’ve got the feeling that this should be fairly easy in Python, but I just don’t see it. Could somebody help me out?

Answer 1

In python 2.6,

import itertools

def intersperse(x, numzeroes):
    for indices in itertools.combinations(range(len(x) + numzeroes), numzeroes):
        y = x[:]
        for i in indices:
            y.insert(0, i)
        yield y

x = [[1, 1, 2], [1, 1, 1, 2], [1, 1, 2]]
list(intersperse(x, 3))