Spirals of numbers

spiral.py

class Turtle:
    directions = [( 0,  1),
                  (-1,  0),
                  ( 0, -1),
                  ( 1,  0)]

    def __init__(self, x=0, y=0, d=0, boundary=lambda x, y: True):
        self.x = x
        self.y = y
        self.d = d
        self.boundary = boundary
        self.tasks = []

    def do_step(self):
        self.x += Turtle.directions[self.d][0]
        self.y += Turtle.directions[self.d][1]
        return self.x, self.y

    def do_left(self):
        self.d = (self.d + 1) % 4

    def do_right(self):
        self.d = (self.d - 1) % 4

    def add_step(self):
        self.tasks.append(self.do_step)

    def add_steps(self, n):
        for _ in range(n):
            self.add_step()

    def add_left(self):
        self.tasks.append(self.do_left)

    def add_right(self):
        self.tasks.append(self.do_right)

    def __iter__(self):
        while self.boundary(self.x, self.y):
            yield self.x, self.y
            if not self.tasks:
                return
            while not self.tasks.pop(0)():
                if not self.tasks:
                    return

def spiral_grid(n):
    grid = [[None for _ in range(n)] for _ in range(n)]
    x, y = n // 2, (n + 1) // 2 - 1
    t = Turtle(x, y, 0, lambda x, y: 0 <= x < n and 0 <= y < n)
    for dist in range(1, n + 1):
        t.add_steps(dist)
        t.add_left()
        t.add_steps(dist)
        t.add_left()
    for i, pos in enumerate(t):
        grid[pos[0]][pos[1]] = i + 1
    return grid

def print_spiral(n, sep='\t'):
    for line in spiral_grid(n):
        print(sep.join(map(str, line)))

if __name__ == '__main__':
    for n in range(1, 10):
        print_spiral(n)
        print()

spiral_output.txt

1

4	3
1	2

5	4	3
6	1	2
7	8	9

16	15	14	13
5	4	3	12
6	1	2	11
7	8	9	10

17	16	15	14	13
18	5	4	3	12
19	6	1	2	11
20	7	8	9	10
21	22	23	24	25

36	35	34	33	32	31
17	16	15	14	13	30
18	5	4	3	12	29
19	6	1	2	11	28
20	7	8	9	10	27
21	22	23	24	25	26

37	36	35	34	33	32	31
38	17	16	15	14	13	30
39	18	5	4	3	12	29
40	19	6	1	2	11	28
41	20	7	8	9	10	27
42	21	22	23	24	25	26
43	44	45	46	47	48	49

64	63	62	61	60	59	58	57
37	36	35	34	33	32	31	56
38	17	16	15	14	13	30	55
39	18	5	4	3	12	29	54
40	19	6	1	2	11	28	53
41	20	7	8	9	10	27	52
42	21	22	23	24	25	26	51
43	44	45	46	47	48	49	50

65	64	63	62	61	60	59	58	57
66	37	36	35	34	33	32	31	56
67	38	17	16	15	14	13	30	55
68	39	18	5	4	3	12	29	54
69	40	19	6	1	2	11	28	53
70	41	20	7	8	9	10	27	52
71	42	21	22	23	24	25	26	51
72	43	44	45	46	47	48	49	50
73	74	75	76	77	78	79	80	81