python-3.6.zip added from Github

README.cosmo contains the necessary links.

third_party/python/Lib/turtledemo/fractalcurves.py

@@ -0,0 +1,138 @@
+#!/usr/bin/env python3
+"""      turtle-example-suite:
+
+        tdemo_fractalCurves.py
+
+This program draws two fractal-curve-designs:
+(1) A hilbert curve (in a box)
+(2) A combination of Koch-curves.
+
+The CurvesTurtle class and the fractal-curve-
+methods are taken from the PythonCard example
+scripts for turtle-graphics.
+"""
+from turtle import *
+from time import sleep, clock
+
+class CurvesTurtle(Pen):
+    # example derived from
+    # Turtle Geometry: The Computer as a Medium for Exploring Mathematics
+    # by Harold Abelson and Andrea diSessa
+    # p. 96-98
+    def hilbert(self, size, level, parity):
+        if level == 0:
+            return
+        # rotate and draw first subcurve with opposite parity to big curve
+        self.left(parity * 90)
+        self.hilbert(size, level - 1, -parity)
+        # interface to and draw second subcurve with same parity as big curve
+        self.forward(size)
+        self.right(parity * 90)
+        self.hilbert(size, level - 1, parity)
+        # third subcurve
+        self.forward(size)
+        self.hilbert(size, level - 1, parity)
+        # fourth subcurve
+        self.right(parity * 90)
+        self.forward(size)
+        self.hilbert(size, level - 1, -parity)
+        # a final turn is needed to make the turtle
+        # end up facing outward from the large square
+        self.left(parity * 90)
+
+    # Visual Modeling with Logo: A Structural Approach to Seeing
+    # by James Clayson
+    # Koch curve, after Helge von Koch who introduced this geometric figure in 1904
+    # p. 146
+    def fractalgon(self, n, rad, lev, dir):
+        import math
+
+        # if dir = 1 turn outward
+        # if dir = -1 turn inward
+        edge = 2 * rad * math.sin(math.pi / n)
+        self.pu()
+        self.fd(rad)
+        self.pd()
+        self.rt(180 - (90 * (n - 2) / n))
+        for i in range(n):
+            self.fractal(edge, lev, dir)
+            self.rt(360 / n)
+        self.lt(180 - (90 * (n - 2) / n))
+        self.pu()
+        self.bk(rad)
+        self.pd()
+
+    # p. 146
+    def fractal(self, dist, depth, dir):
+        if depth < 1:
+            self.fd(dist)
+            return
+        self.fractal(dist / 3, depth - 1, dir)
+        self.lt(60 * dir)
+        self.fractal(dist / 3, depth - 1, dir)
+        self.rt(120 * dir)
+        self.fractal(dist / 3, depth - 1, dir)
+        self.lt(60 * dir)
+        self.fractal(dist / 3, depth - 1, dir)
+
+def main():
+    ft = CurvesTurtle()
+
+    ft.reset()
+    ft.speed(0)
+    ft.ht()
+    ft.getscreen().tracer(1,0)
+    ft.pu()
+
+    size = 6
+    ft.setpos(-33*size, -32*size)
+    ft.pd()
+
+    ta=clock()
+    ft.fillcolor("red")
+    ft.begin_fill()
+    ft.fd(size)
+
+    ft.hilbert(size, 6, 1)
+
+    # frame
+    ft.fd(size)
+    for i in range(3):
+        ft.lt(90)
+        ft.fd(size*(64+i%2))
+    ft.pu()
+    for i in range(2):
+        ft.fd(size)
+        ft.rt(90)
+    ft.pd()
+    for i in range(4):
+        ft.fd(size*(66+i%2))
+        ft.rt(90)
+    ft.end_fill()
+    tb=clock()
+    res =  "Hilbert: %.2fsec. " % (tb-ta)
+
+    sleep(3)
+
+    ft.reset()
+    ft.speed(0)
+    ft.ht()
+    ft.getscreen().tracer(1,0)
+
+    ta=clock()
+    ft.color("black", "blue")
+    ft.begin_fill()
+    ft.fractalgon(3, 250, 4, 1)
+    ft.end_fill()
+    ft.begin_fill()
+    ft.color("red")
+    ft.fractalgon(3, 200, 4, -1)
+    ft.end_fill()
+    tb=clock()
+    res +=  "Koch: %.2fsec." % (tb-ta)
+    return res
+
+if __name__  == '__main__':
+    msg = main()
+    print(msg)
+    mainloop()