Matrix spiral print

spiral.py

def spiral(M):
    """
    Given a matrix M (mxn) print out the elements in spiral order

    Ex:

    30 42 30 55 31
    21 30 60 24 38
    11 22 33 44 55

    prints:

    30 42 30 55 31 38 55 44 33 22 11 21 30 60 24

    """

    m = len(M)
    n = len(M[0])

    total_elements = m * n

    s = 0 # top boundary of the matrix
    e = m-1 # bot boundary of the matrix

    l = 0
    r = n-1

    elems = []

    # bulk of the body
    while True:
        # print s, e, l, r
        # top row right
        for j in xrange(s, r):
            elems.append(M[s][j])

        if len(elems) >= total_elements:
            break

        # right col up
        for i in xrange(s, e+1):
            elems.append(M[i][r])

        if len(elems) >= total_elements:
            break

        # bot row left
        for j in xrange(r-1, l, -1):
            elems.append(M[e][j])

        if len(elems) >= total_elements:
            break

        # left col down
        for i in xrange(e, s, -1):
            elems.append(M[i][l])

        if len(elems) >= total_elements:
            break

        s += 1
        e -= 1
        l += 1
        r -= 1

    return elems

M1 = [[30, 42, 30, 55, 31],
    [21, 30, 60, 24, 38],
    [11, 22, 33, 44, 55],]
M2 = [[1,2,3,4,5],
    [16,17,18,19,6],
    [15, 24, 25, 20, 7],
    [14, 23, 22, 21, 8],
    [13, 12, 11, 10, 9]]
M3 = [[1,2,3,4,5]]
M4 = [[1,2,3,4,5],
      [10, 9, 8, 7, 6]]
M5 = [[1,2],
      [10,3],
      [9, 4],
      [8, 5],
      [7, 6]]

A1 = [30, 42, 30, 55, 31, 38, 55, 44, 33, 22, 11, 21, 30, 60 ,24]
A2 = [i for i in range(1, 26)]
A3 = [1,2,3,4,5]
A4 = [i for i in range(1, 11)]
A5= [i for i in range(1, 11)]

assert(spiral(M1) == A1)
assert(spiral(M2) == A2)
assert(spiral(M3) == A3)
assert(spiral(M4) == A4)
assert(spiral(M5) == A5)