Rockin' Robin from Code Wars https://www.codewars.com/kata/580ee4f2df9127927c0000be

rockin_robin.py

arrays = [ [1,7], [2,3,4], [10,11,12,13] ]

while arrays:
    for (index, item) in enumerate(arrays):
        if len(arrays[index]) == 0:
            arrays.pop(index)
            continue
        print arrays[index].pop(0)
        print arrays

1
2
10
7
3
11
12
4
13

Visualizing the array shrinkage:

1
[[7], [2, 3, 4], [10, 11, 12, 13]]
2
[[7], [3, 4], [10, 11, 12, 13]]
10
[[7], [3, 4], [11, 12, 13]]
7
[[], [3, 4], [11, 12, 13]]
3
[[], [4], [11, 12, 13]]
11
[[], [4], [12, 13]]
12
[[4], [13]]
4
[[], [13]]
13
[[], []]