"""File:      koch_curve.py
   Purpose:   Use TurtleWorld to draw a Koch curve

   Run:       python koch_curve.py

   Input:     The ``length'' of the curve.
   Output:    A TurtleWorld window with a Koch curve.

   Note:      This is a slightly modified version of the
              solution to the Koch curve exercise in
              Think Python: An Introduction to Software Design,
              Allen B. Downey
   Note:      The ``stretch'' argument can be used to enlarge
              the curve when n is small.
"""
from TurtleWorld import *

def koch(t, n, stretch):
   """Draw a Koch curve having "length" n with turtle t
      stretch is used to increase the actual length of the
      curve when n is small"""
   if n < 3:
      fd(t, stretch)
      return
   m = n/3.0
   koch(t, m, stretch/3.0)
   lt(t, 60)
   koch(t, m, stretch/3.0)
   rt(t, 120)
   koch(t, m, stretch/3.0)
   lt(t, 60)
   koch(t, m, stretch/3.0)

def to_lower_left_corner(t):
   """Move t to the lower left corner of the window without drawing"""
   pu(t)
   rt(t)
   fd(t,200)
   rt(t)
   fd(t,200)
   rt(t)
   rt(t)
   pd(t)

#----------------------------------------------------------------------
# Main program
world = TurtleWorld()
bob = Turtle()
bob.delay = 0
to_lower_left_corner(bob)

n = int(raw_input("How long should the curve be?\n   "))

koch(bob, n, 400)

wait_for_user()