问为什么我的turtle会有报错？

import turtle as t
import time
import random

p1="pink"
g1="green"
b="blue"
y="yellow"
r="red"
p2="purple"
g2="grey"
o="orange"

rand=""

def ran():
    global rand
    r=random.randint(1,8)
    if r==1:
        rand=p1
    elif r==2:
        rand=p2
    elif r==3:
        rand=g1
    elif r==4:
        rand=g2
    elif r==5:
        rand=b
    elif r==6:
        rand=o
    elif r==7:
        rand=r
    else:
        rand=y

def wri(x,y,n,r=rand):
    t.penup()
    t.color(r)
    t.goto(x,y)
    t.pendown()
    t.write(n,font=("楷书",20))

wri(0,0,"解")
time.sleep(0.5)
wri(0,0,"落")

t.done()