为什么会有“cannot unpack non-iterable NoneType object”的报错？

Question

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

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

t.done()

Answer 1

因为颜色没有啊大哥, 虽然你申明了一个全局变量, 但是你如果不去调用ran() 函数, 你的颜色值 是不能赋值给 rand 的