求助，turtle画蛇报错

import turtle
def drawsnake(rad,angle,len,neckrad):
for i in range(len):
turtle.circle(rad,angle)
turtle.circle(-rad,angle)
turtle.circle(rad,angle/2)
turtle.fd(rad)
turtle.circle(neckrad+1,180)
turtle.fd(rad*2/3)
def main():
turtle.setup(1300,800,0,0)
pythonsize = 30
turtle.pensize(pythonsize)
turtle.pencolor('bule')
turtle.seth(-40)
drawsnake(40,80,5,pythonsize/2)
main()

第11行，setup改成goto