""" turtle-example-suite:

 tdemo_round_dance.py

(Needs version 1.1 of the turtle module that
comes with Python 3.1)

Dancing turtles have a compound shape
consisting of a series of triangles of
decreasing size.

Turtles march along a circle while rotating
pairwise in opposite direction, with one
exception. Does that breaking of symmetry
enhance the attractiveness of the example?

Press any key to stop the animation.

Technically: demonstrates use of compound
shapes, transformation of shapes as well as
cloning turtles. The animation is
controlled through update().
"""

from turtle import *

def stop():
 global running
 running = False

def main():
 global running
 clearscreen()
 bgcolor("gray10")
 tracer(False)
 shape("triangle")
 f = 0.793402
 phi = 9.064678
 s = 5
 c = 1
 # create compound shape
 sh = Shape("compound")
 for i in range(10):
 shapesize(s)
 p =get_shapepoly()
 s *= f
 c *= f
 tilt(-phi)
 sh.addcomponent(p, (c, 0.25, 1-c), "black")
 register_shape("multitri", sh)
 # create dancers
 shapesize(1)
 shape("multitri")
 pu()
 setpos(0, -200)
 dancers = []
 for i in range(180):
 fd(7)
 tilt(-4)
 lt(2)
 update()
 if i % 12 == 0:
 dancers.append(clone())
 home()
 # dance
 running = True
 onkeypress(stop)
 listen()
 cs = 1
 while running:
 ta = -4
 for dancer in dancers:
 dancer.fd(7)
 dancer.lt(2)
 dancer.tilt(ta)
 ta = -4 if ta > 0 else 2
 if cs < 180:
 right(4)
 shapesize(cs)
 cs *= 1.005
 update()
 return "DONE!"

if __name__=='__main__':
 print(main())
 mainloop()