#!/usr/bin/env python3
""" turtle-example-suite:

 tdemo_tree.py

Displays a 'breadth-first-tree' - in contrast
to the classical Logo tree drawing programs,
which use a depth-first-algorithm.

Uses:
(1) a tree-generator, where the drawing is
quasi the side-effect, whereas the generator
always yields None.
(2) Turtle-cloning: At each branching point
the current pen is cloned. So in the end
there are 1024 turtles.
"""
from turtle import Turtle, mainloop
from time import perf_counter as clock

def tree(plist, l, a, f):
 """ plist is list of pens
 l is length of branch
 a is half of the angle between 2 branches
 f is factor by which branch is shortened
 from level to level."""
 if l > 3:
 lst = []
 for p in plist:
 p.forward(l)
 q = p.clone()
 p.left(a)
 q.right(a)
 lst.append(p)
 lst.append(q)
 for x in tree(lst, l*f, a, f):
 yield None

def maketree():
 p = Turtle()
 p.setundobuffer(None)
 p.hideturtle()
 p.speed(0)
 p.getscreen().tracer(30,0)
 p.left(90)
 p.penup()
 p.forward(-210)
 p.pendown()
 t = tree([p], 200, 65, 0.6375)
 for x in t:
 pass

def main():
 a=clock()
 maketree()
 b=clock()
 return "done: %.2f sec." % (b-a)

if __name__ == "__main__":
 msg = main()
 print(msg)
 mainloop()