Python Turtle World : chapter 4

1. PythonTurtle World : chapter 4 From Think Python How to Think Like a Computer Scientist

2. Download Swampy • Swampy is a collection of python files/libs that create a Logo like turtle environment. • You first need to download the files from • http://www.greenteapress.com/thinkpython/swampy/ • Click on Install Swampy and do the appropriate install based on your OS. It also requires the installation of Tkinter • I download swampy-2.1.7.zip • Decompress and move swampy directory to • C:\Python27\Lib\site-packages\ if you are using Python 2.7.6 • Note: You can do all this in Linux, Macintosh or Windows

3. Test Swampy • Run the python GUI and create a new file and save it in a directory of your choice testit.py. Pick a directory name like pythonPrograms • Type in the following program and run it • You should get a popup window that that shown on the right. • The little turtle has drawn a square

4. Test Program Required for this lab only! • import sys • sys.path.append("Y:\Bolin College of Science and Mathematics\Richard Simpson\site-packages") • #Test TurtleWorld • from swampy.TurtleWorld import * • world = TurtleWorld() • bob = Turtle()  Create a turtle named bob. Initial heading is east i.e. 0 • bob.delay=.01 • fd(bob,100) • rt(bob,90) • fd(bob,100) • rt(bob,90) • fd(bob,100) • rt(bob,90) • fd(bob,100) • wait_for_user() 90 heading 180 0 270

5. Turtle Commands • bk(self, dist=1) unbound Turtlemethod • Moves the turtle backward by the given distance. • fd(self, dist=1) unbound Turtlemethod • Moves the turtle foward by the given distance. • lt(self, angle=90) unbound Turtle • methodTurns left by the given angle. • pd(self) unbound Turtlemethod • Puts the pen down (active). • pu(self) unbound Turtlemethod • Puts the pen up (inactive). • rt(self, angle=90) unbound Turtlemethod • Turns right by the given angle. • set_color(self, color) unbound Turtlemethod • Changes the color of the turtle.

6. More Commandshttp://www.greenteapress.com/thinkpython/swampy/TurtleWorld.html Attributes: x: position  y: position r: radius of shellheading: what direction the turtle is  facing, in degrees.  0 is east. pen:boolean, whether the pen is downcolor: string turtle color delay: delay between instructions The can be set directly For example self.x = 10 • draw(self) • Draws the turtle. • get_heading(self) • Returns the current heading in degrees.  0 is east. • get_x(self) • Returns the current x coordinate. • get_y(self) • Returns the current y coordinate. • set_pen_color(self, color) • Changes the pen color of the turtle. • step(self) • Takes a step. Default step behavior is forward one pixel. • die(self) • Removes the animal from the world and undraws it. • undraw(self) • Undraws the animal.

7. Lets draw a square with a loop • from swampy.TurtleWorldimport * • world = TurtleWorld() • bob = Turtle()  Create a turtle named bob. Initial heading is east i.e. 0 and initial location is at (0,0) • bob.delay=.01 • for i in range(4):  This is the for loop • fd(bob,100) • rt(bob, 90) • wait_for_user() These 2 instructions are performed 4 times Four space indention is required!!!

8. Lets draw things • Write a program to draw each of the following. Use for loop! • 2. • 3. 4. Remember you can bob.x=0 and bob.y=0

9. Lets use functions to help us here • Fill in the following function so that it draws a square when called. It has to parameters self and length. Self is the turtle name and length is the length of the edge of the square • def square(self, length): • fd(self,length) • rt(self, 90) • # Run it • square(bob,200) • #type this in and test it out.

10. How about drawing a regular polygon of n sides? • If N = 6 What is this angle? What is the angle in terms of N? 360.0/N

11. Complete the Following • def polygon(self, n, length) • angle = 360.0/n • for i in range(n): • fd(self,length) • rt(self,angle) • # call it • polygon(bob, 6) • # Advanced problem: Change this so the polygon is drawn centered in the window!!!

12. Draw a circle of radius r!!!! • We will approximate this with the polygon() function we already wrote. • def circle(self, radius) • How can we use C = 2πr to help us here? • Hint: as the value of n ( number of sides of the polygon) gets large n*length_of_edge ≈ C (Do you agree?) • So Pick n to be C/length_of_edge • where length_of_edge = 3 (some small value) • This way we use only enough edges as are needed!!!

13. Simulating a random moving turtle • In this project we will first develop a turtle program that creates a turtle the moves around randomly. • We first have to pick a random direction the turn to. • Python has a built in function called random. We can use it by importing it • from random import * • Here is an example that returns a number from 0 to 1 • x = random() • If we want a random number from 0 to 100 we could • x = random()*100

14. The Code • from swampy.TurtleWorld import * • from random import * • world = TurtleWorld() • bob = Turtle() • bob.delay=.01 • for i in range(1000): # 1000 random steps • fd( bob,3) • # the following creates a random • # number from -45 to +45 • angle = random()*90-45 • rt(bob,angle) • die(bob) • wait_for_user() 300 steps example