snail_sort_1line.py

def snail(array):
    return list(array[0]) + snail(zip(*array[1:])[::-1]) if array else []
        

# Tests 

array = [[]]
expected = []
test.assert_equals(snail(array), expected)

array = [[1,2,3],
         [4,5,6],
         [7,8,9]]
expected = [1,2,3,6,9,8,7,4,5]
test.assert_equals(snail(array), expected)


array = [[1,2,3],
         [8,9,4],
         [7,6,5]]
expected = [1,2,3,4,5,6,7,8,9]
test.assert_equals(snail(array), expected)

array = [[1,2,3,4],
         [5,6,7,8],
         [9,10,11,12],
         [13,14,15,16]]
expected = [1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10]
test.assert_equals(snail(array), expected)