these are some exercises from the think like a copmuter scientist book.
	new file:   turtles_4_funct_4.9.ex1.py
	new file:   turtles_4_funct_4.9.ex2.py
	new file:   turtles_4_funct_4.9.ex3.py
	new file:   turtles_4_funct_4.9.ex4.py