import math

import turtle

def square(t, length):

? ? """Draws a square with sides of the given length.

? ? Returns the Turtle to the starting position and location.

? ? """

? ? for i in range(4):

? ? ? ? t.fd(length)

? ? ? ? t.lt(90)

def polyline(t, n, length, angle):

? ? """Draws n line segments.

? ? t: Turtle object

? ? n: number of line segments

? ? length: length of each segment

? ? angle: degrees between segments

? ? """

? ? for i in range(n):

? ? ? ? t.fd(length)

? ? ? ? t.lt(angle)

def polygon(t, n, length):

? ? """Draws a polygon with n sides.

? ? t: Turtle

? ? n: number of sides

? ? length: length of each side.

? ? """

? ? angle = 360.0/n

? ? polyline(t, n, length, angle)

def arc(t, r, angle):

? ? """Draws an arc with the given radius and angle.

? ? t: Turtle

? ? r: radius

? ? angle: angle subtended by the arc, in degrees

? ? """

? ? arc_length = 2 * math.pi * r * abs(angle) / 360

? ? n = int(arc_length / 4) + 1

? ? step_length = arc_length / n

? ? step_angle = float(angle) / n

? ? # making a slight left turn before starting reduces

? ? # the error caused by the linear approximation of the arc

? ? t.lt(step_angle/2)

? ? polyline(t, n, step_length, step_angle)

? ? t.rt(step_angle/2)

def circle(t, r):

? ? """Draws a circle with the given radius.

? ? t: Turtle

? ? r: radius

? ? """

? ? arc(t, r, 360)

# the following condition checks whether we are

# running as a script, in which case run the test code,

# or being imported, in which case don't.

if __name__ == '__main__':

? ? bob = turtle.Turtle()

? ? # draw a circle centered on the origin

? ? radius = 100

? ? bob.pu()

? ? bob.fd(radius)

? ? bob.lt(90)

? ? bob.pd()

? ? circle(bob, radius)

? ? # wait for the user to close the window

? ? turtle.mainloop()

#你從命令指示符里面運行一下試試