spiraling number in python

spiral.py

class Spiral(object):
    def __init__(self, xsize=4, ysize=None):
        self.xsize = xsize
        self.ysize = xsize if ysize is None else ysize
        self.x = 0 
        self.y = -1
        self.vx = 0 
        self.vy = 1 
        self.max = self.xsize * self.ysize
        self.init_board()
        self.num = 1 

    def init_board(self):
        self.board = []
        for x in xrange(self.xsize):
            self.board.append([])
            for y in xrange(self.ysize):
                self.board[x].append(0)

    def move(self):
        next_x = self.x + self.vx
        next_y = self.y + self.vy
        if next_y < 0 or next_y >= self.ysize or next_x < 0 or next_x >= self.xsize or self.board[next_x][next_y] != 0:
                self.vx, self.vy = self.vy, self.vx * -1

        self.x = self.x + self.vx
        self.y = self.y + self.vy
        print 'position:',self.x,self.y,'vector:',self.vx,self.vy


    def populate(self):
        while (self.num <= self.max):
            self.move()
            self.board[self.x][self.y] = self.num
            self.num += 1

    def draw(self):
        self.populate()
        for x in self.board:
            for y in x:
                    print "{:5}".format(y),
            print    

Spiral(5,6).draw()