Python Turtle Graphics ASFA CS Principles 2015 2016

Python Turtle Graphics ASFA CS Principles 2015 -2016

A first Object: Logo Turtle • Dr. Seymour Papert at MIT invented the Turtle as a graphical and mathematical object to think with for the children’s programming language, Logo (1966)

Robot Turtles • Children programmed robot turtles to draw pictures

• A turtle is an object. – Every turtle understands the same methods. – Every turtle has the same fields or instance variables. • Heading, body color, pen color, X and Y position. • Yet each turtle can have its own values for these fields. • Many modern programming languages, such as Python, continue to use turtles for drawing

• Think of a turtle crawling on a piece of paper, with a pen tied to its tail – Sheet of paper is a window on a display screen – Position specified with (x, y) coordinates • Cartesian coordinate system, with origin (0, 0) at the center of a window

• Imagine a turtle starting at (0, 0) – Give it the command turtle. forward(15), and it moves (on-screen) 15 pixels in the direction it is facing, drawing a line as it moves. – Give it the command turtle. left(25), and it rotates in-place 25 degrees counter-clockwise.

Some Examples of Turtle Programs • A forest scene created with turtles • http: //www. youtube. com/watch? v=Wwzv 0 F WJ 5 g. Q • A Recursive Turtle Drawing Program • http: //www. youtube. com/watch? feature=pla yer_embedded&v=Yummtrv. NC 2 o

Some Key Methods from turtle import * # pen/turtle starts at the center (x=0, y=0) of the turtle display area shape(“turtle”) color("green") # pen up, don't draw up() # centers the circle goto(0, -50) # pen down, draw down() # radius=50 center is 50 radius units above the turtle circle(50) up() # center the turtle again goto(0, 0) down() tur 2. py

Turtle drawing with repetition from turtle import * def star(): color('red', 'purple') colormode(255) begin_fill() for i in range(36): pencolor(3*i + 100, 0 , 5*i) forward(200) left(85) forward(10) left(45) forward(40) left(-90) forward(40) left(85) forward(10) left(45) end_fill() setpos(100, 45) color("white", "yellow") shape("turtle") star() spyro. py

Recursive Drawing Algorithms Recursive Algorithms are used to create fractals

Documentation available explaining methods available • If you have trouble getting the docs from Python, you can go to http: //docs. python. org/library/turtle. html

Turtle library contains many methods

Click on method you want to see

Method usage documentation and examples

Endless Artistic Possibilities

What can you create?

Assignment • Explore the documentation • Design and program a turtle drawing a picture Must include: • • At least 4 colors At least 4 shapes A filled object Looping • Show me the drawing creation • Email your program to me after checked off • Make a multi-turtle program if you are done