python绘制螺旋线

#coding=utf-8
from math import sqrt,cos,sin
import Image, ImageDraw
class SpireShape(object):
    def __init__(self, draw):
        self.draw = draw
        self.line_width = 1
        self.line_color = (0,0,0)
        self.current_point = (0, 0)
    def setPoints(self,points):
        self.points = points
    def setLineWidth(self,line_width):
        self.line_width = line_width
    def setLineColor(self,line_color):
        self.line_color = line_color
   
    def moveto(self, p):
        self.current_point = p
   
    def lineto(self, p):
        self.draw.line((self.current_point, p), width=self.line_width, fill=self.line_color)
        self.current_point = p
    def point(self, p):
        self.draw.point(p,fill=self.line_color)
        self.current_point = p
    def spire(self, p, angle,rate):
        '''
        p is start point,angle is start angle,rate is scatter speed len/thita.
            '''
        r = 0;
        thita = 0;
        pi = 3.14
        du = 2*pi/360
        while r<=500.0:
            posX =