lissajous curve generator

from Tkinter import *
from math import sin, cos
width = 640
height = 480
w = Canvas(Tk(), width=width, height=height)
w.pack()
t = 0.0
step = 1
a = 10.5
b = 11
def pos(t):
    x = width/2 + (width * sin( t/a )) * 0.49
    y = height/2 + (height * cos( t/b )) * 0.49
    return x, y
def draw(t):
    p1, p2 = pos(t), pos(t + step)
    w.create_line(p1[0], p1[1], p2[0], p2[1])
while 1:
    draw(t)
    t += step
    w.update()