《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 object19     n: number of line segments20     length: length of each segment21     angle: degrees between segments22     """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: Turtle32     n: number of sides33     length: length of each side.34     """35     angle = 360.0/n36     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: Turtle43     r: radius44     angle: angle subtended by the arc, in degrees45     """46     arc_length = 2 * math.pi * r * abs(angle) / 36047     n = int(arc_length / 4) + 148     step_length = arc_length / n49     step_angle = float(angle) / n50 51     # making a slight left turn before starting reduces52     # the error caused by the linear approximation of the arc53     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: Turtle62     r: radius63     """64     arc(t, r, 360)65 66 # the following condition checks whether we are67 # 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 origin74     radius = 10075     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 window82     turtle.mainloop()

#flower.pyimport turtlefrom 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()