"""This module contains a code example related to
Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com
Copyright 2015 Allen Downey
License: http://creativecommons.org/licenses/by/4.0/
"""
from __future__ import print_function, division
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()