《像计算机科学家一样思考PYTHON》练习4-2
http://www.greenteapress.com/thinkpython2/code/flower.py
附图
1 #mypolygon.py 2 import turtle 3 import math 4 5 def square(t, length): 6 """Draws a square with sides of the given length. 7 8 Returns the Turtle to the starting position and location. 9 """ 10 for i in range(4): 11 t.fd(length) 12 t.lt(90) 13 14 15 def polyline(t, n, length, angle): 16 """Draws n line segments. 17 18 t: Turtle object 19 n: number of line segments 20 length: length of each segment 21 angle: degrees between segments 22 """ 23 for i in range(n): 24 t.fd(length) 25 t.lt(angle) 26 27 28 def polygon(t, n, length): 29 """Draws a polygon with n sides. 30 31 t: Turtle 32 n: number of sides 33 length: length of each side. 34 """ 35 angle = 360.0/n 36 polyline(t, n, length, angle) 37 38 39 def arc(t, r, angle): 40 """Draws an arc with the given radius and angle. 41 42 t: Turtle 43 r: radius 44 angle: angle subtended by the arc, in degrees 45 """ 46 arc_length = 2 * math.pi * r * abs(angle) / 360 47 n = int(arc_length / 4) + 1 48 step_length = arc_length / n 49 step_angle = float(angle) / n 50 51 # making a slight left turn before starting reduces 52 # the error caused by the linear approximation of the arc 53 t.lt(step_angle/2) 54 polyline(t, n, step_length, step_angle) 55 t.rt(step_angle/2) 56 57 58 def circle(t, r): 59 """Draws a circle with the given radius. 60 61 t: Turtle 62 r: radius 63 """ 64 arc(t, r, 360) 65 66 # the following condition checks whether we are 67 # running as a script, in which case run the test code, 68 # or being imported, in which case don't. 69 70 if __name__ == '__main__': 71 bob = turtle.Turtle() 72 73 # draw a circle centered on the origin 74 radius = 100 75 bob.pu() 76 bob.fd(radius) 77 bob.lt(90) 78 bob.pd() 79 arc(bob, radius,100) 80 81 # wait for the user to close the window 82 turtle.mainloop()
#flower.py import turtle from mypolygon import arcdef move(t, length): t.pu() t.fd(length) t.pd() def petal(t, r, angle):#绘制花瓣 for i in range(2): arc(t, r, angle) t.lt(180-angle) def flower(t, n, r, angle): for i in range(n): petal(t, r, angle) t.lt(360.0/n) bob = turtle.Turtle() move(bob, -100) flower(bob, 7, 60.0, 60.0) move(bob, 100) flower(bob, 10, 40.0, 80.0) move(bob, 100) flower(bob, 20, 140.0, 20.0) bob.hideturtle() turtle.mainloop()
