python-3.6.zip added from Github

README.cosmo contains the necessary links.

third_party/python/Lib/turtledemo/lindenmayer.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+"""       turtle-example-suite:
+
+        xtx_lindenmayer_indian.py
+
+Each morning women in Tamil Nadu, in southern
+India, place designs, created by using rice
+flour and known as kolam on the thresholds of
+their homes.
+
+These can be described by Lindenmayer systems,
+which can easily be implemented with turtle
+graphics and Python.
+
+Two examples are shown here:
+(1) the snake kolam
+(2) anklets of Krishna
+
+Taken from Marcia Ascher: Mathematics
+Elsewhere, An Exploration of Ideas Across
+Cultures
+
+"""
+################################
+# Mini Lindenmayer tool
+###############################
+
+from turtle import *
+
+def replace( seq, replacementRules, n ):
+    for i in range(n):
+        newseq = ""
+        for element in seq:
+            newseq = newseq + replacementRules.get(element,element)
+        seq = newseq
+    return seq
+
+def draw( commands, rules ):
+    for b in commands:
+        try:
+            rules[b]()
+        except TypeError:
+            try:
+                draw(rules[b], rules)
+            except:
+                pass
+
+
+def main():
+    ################################
+    # Example 1: Snake kolam
+    ################################
+
+
+    def r():
+        right(45)
+
+    def l():
+        left(45)
+
+    def f():
+        forward(7.5)
+
+    snake_rules = {"-":r, "+":l, "f":f, "b":"f+f+f--f--f+f+f"}
+    snake_replacementRules = {"b": "b+f+b--f--b+f+b"}
+    snake_start = "b--f--b--f"
+
+    drawing = replace(snake_start, snake_replacementRules, 3)
+
+    reset()
+    speed(3)
+    tracer(1,0)
+    ht()
+    up()
+    backward(195)
+    down()
+    draw(drawing, snake_rules)
+
+    from time import sleep
+    sleep(3)
+
+    ################################
+    # Example 2: Anklets of Krishna
+    ################################
+
+    def A():
+        color("red")
+        circle(10,90)
+
+    def B():
+        from math import sqrt
+        color("black")
+        l = 5/sqrt(2)
+        forward(l)
+        circle(l, 270)
+        forward(l)
+
+    def F():
+        color("green")
+        forward(10)
+
+    krishna_rules = {"a":A, "b":B, "f":F}
+    krishna_replacementRules = {"a" : "afbfa", "b" : "afbfbfbfa" }
+    krishna_start = "fbfbfbfb"
+
+    reset()
+    speed(0)
+    tracer(3,0)
+    ht()
+    left(45)
+    drawing = replace(krishna_start, krishna_replacementRules, 3)
+    draw(drawing, krishna_rules)
+    tracer(1)
+    return "Done!"
+
+if __name__=='__main__':
+    msg = main()
+    print(msg)
+    mainloop()