Iterate a 2d matrix using a spiral pattern

spiral.py

import unittest
import copy
from itertools import cycle


def row(matrix, n):
    # returns row n of a 2d matrix
    return matrix.pop(n)


def col(matrix, n):
    # returns column n of a 2d matrix
    return [row.pop(n) for row in matrix]


def rev(f):
    # return a function such that rev(f) equals the reverse of the results of f
    def mapped(*a, **kw):
        return reversed(f(*a, **kw))
    return mapped


def spiral(matrix):
    # avoid mutating our caller's matrix
    matrix = copy.deepcopy(matrix)

    slice = cycle([row, col, rev(row), rev(col)])
    side = cycle([0, -1, -1, 0])

    # alternate between slicing rows and columns, and first and final side until
    # the matrix has been consumed
    while matrix:
        for item in slice.next()(matrix, side.next()):
            yield item


class TestSpiral(unittest.TestCase):
    def test_input1(self):
        input1 = [
            [0,  1,  2,  3],
            [4,  5,  6,  7],
            [8,  9,  10, 11],
            [12, 13, 14, 15], ]

        output1 = [0, 1, 2, 3, 7, 11, 15, 14, 13, 12, 8, 4, 5, 6, 10, 9]

        self.assertEqual(list(spiral(input1)), output1)

    def test_input2(self):
        input2 = [
            [0,  1,  2,  3,  4],
            [5,  6,  7,  8,  9],
            [10, 11, 12, 13, 14],
            [15, 16, 17, 18, 19],
            [20, 21, 22, 23, 24], ]

        output2 = [
            0, 1, 2, 3, 4, 9, 14, 19, 24, 23, 22, 21, 20, 15, 10, 5, 6, 7, 8,
            13, 18, 17, 16, 11, 12,]

        self.assertEqual(list(spiral(input2)), output2)


if __name__ == '__main__':
    unittest.main()