python 3.4 spirograph error -

from turtle import*                                                                       math import*  def xcord(r,r,p,t):        x= (r-r) * cos(t) - (r+p) * cos((r-r)//r*t)  def ycord (r,r,p,t):      y= (r-r) * sin(t) - (r+p) * sin((r-r)//r*t)  def t_iter(r,r,p):        t=0       down()       goto(xcord(r,r,p,t),ycord(r,r,p,t))       while (t < 2 * pi):           t = t+.01           xcord(r,r,p,t)           ycord(r,r,p,t)           up()       return  def main():        r=100       r=4       p=int(input("please enter number between 10 , 100: "))       if p < 10 or p > 100:             input(" incorrect value of p!")       t_iter(r,r,p)       input("hit enter close porgram")       bye()  main() 

i error:

traceback (most recent call last):    file "c:/users/coscio/desktop/spirals.py", line 31, in <module>     main()    file "c:/users/coscio/desktop/spirals.py", line 27, in main     t_iter(r,r,p)    file "c:/users/coscio/desktop/spirals.py", line 13, in t_iter     goto(xcord(r,r,p,t),ycord(r,r,p,t))    file "<string>", line 1, in goto    file "d:\python\lib\turtle.py", line 1774, in goto     self._goto(vec2d(*x))  typeerror: type object argument after * must sequence, not nonetype 

from turtle import*  math import*  def xcord(r,r,p,t):          return (r-r) * cos(t) - (r+p) * cos((r-r)//r*t)  def ycord (r,r,p,t):     return (r-r) * sin(t) - (r+p) * sin((r-r)//r*t)  def t_iter(r,r,p):     t=0     up()     xcord(r,r,p,t)     ycord(r,r,p,t)     while (t < 2 * pi):         t = t+.01         goto(xcord(r,r,p,t),ycord(r,r,p,t))         down()     return float(xcord(r,r,p,t))     return float(ycord(r,r,p,t))  def validate():     while true:         p=int(input("please enter number between 10 , 100: "))         if p >= 10 or p <= 100:             break     return p   def main():     speed(0)     r=100     r=4     p = validate()     t_iter(r,r,p)     xcord(r,r,p,t_iter(r,r,p))     ycord(r,r,p,t_iter(r,r,p))     input("hit enter close porgram")     bye()  main()