1. Description

Fibonacci sequence is a sequence as below 1, 1, 2, 3, 5, 8, 13, 21 ... Starting from the third item，each item equals the sum of previous two items

With Python's turtle library, we plot the Fibonacci sequence to a curve (Fibonacci Spiral), which is very common in the real world

The Fibonacci Spiral looks like this

Each side length of squares, and the radius of arcs are items in Fibonacci sequence 1, 1, 2, 3, 5, 8, 13, 21 ...

Copy the code below, and write your code after TODO

import turtle

# 可以用来整体调整线条的长度
LENGTH = 10

# 产生 Fibonacci 数列
def fibonacci(n):
    x, y = 0, 1
    for i in range(n):
        if x > 0:
            yield x
        y, x = x, x + y

plt = turtle.Turtle()
plt.speed(50)

for i in fibonacci(10):
    # TODO: complete your code here
    # print(i)

2. About Turtle

With turtle, we can control a pen to plot in Python. You may use the following pen-control methods in thie question.

• plt.pencolor(color), assign the pen color, e.g. "blue", "red", "yellow"
• plt.forward(x) move forward to plot / plt.backward(x) move backward to plot. Use x to set the length of the line
• plt.left(angle) turn left / plt.right(angle) turn right. Use angle to set the angle of the turn
• plt.circle(radius, angle) plot a circle. Use radius to set circle radius，and use angle to plot partial
  • 90 means quarter-circle
  • 180 means semi-circle
  • 360 means full-circle

3. Submission

• Finish your code in Lecture Note
• Click the "递交 / Submit" button on the right，paste your code and submit
• You can ignore the error report after submission (because the teacher didn't set auto-rating for this problem)