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作品效果如下：

源代码：

import turtle

__Pen = turtle.Pen()


__Pen.speed(0)
x = 20
i = 0
__Pen.penup()
__Pen.goto((-100), (-100))
__Pen.pendown()
__Pen.left(90)
while i <= 1200:
    if i % 3 == 0:
        __Pen.pencolor('red')
    elif i % 2 == 0:
        __Pen.pencolor('green')
    else:
        __Pen.pencolor('blue')
    __Pen.forward(x)
    __Pen.right(x)
    i += 1
    if x >= 0 and x >= 30:
        x -= 1
    else:
        x += 100

请多多指教！