文件操作

fr = open('letter.txt',mode='r',encoding='utf-8')
plaincode = fr.read()
print('明文：'+ plaincode)

print('密文',end='')
for c in plaincode:
    print(chr(ord(c)+3),end='')

turtle.speed(10)
colors = ['red', 'purple', 'blue', 'green', 'yellow', 'orange']

for i in range(150):
    turtle.pencolor(colors[i% 6])
    turtle.forward(i)
    turtle.left(70)
turtle.done()