Introduction to Turtle Graphics in Python

by K. Yue

1. Turtle Graphics

• The Python turtle module is a built-in library that provides a way to create graphics and drawings.
• In turtle graphics, there are two major concepts:
  1. A window/screen/digit canvas for the turtle to move and draw.
  2. A turtle with a pen that can move and draw (if the pen is down).

Turtle:

1. The turtle is:
   1. in a co-ordinate location (x,y), initially (0,0)
   2. facing a direction (initially right)
   3. holding a pen which can be up and down (initially down). If the pen is down, the turtle draws while moving.
2. There are functions to control the turtle. Two popular ones are:
   1. forward(distance): move the turtle forward by a distance. If the pen is down, the turtle also draws.
   2. right(degree): turn its face to right with a degree.

Example:

Consider square.py.txt (remove .txt when download):

import turtle

# Create a screen object in turtle
screen = turtle.Screen()

# Set screen dimensions
screen.setup(width=300, height=300)

# Set background color
screen.bgcolor("lightyellow")

# Create a turtle object
pen = turtle.Turtle()
pen.shape("turtle") # Change the turtle's shape
pen.color("green") # Set the turtle's color
pen.pensize(3) # Set the pen's size

pen.forward(100) # Move forward by 100 units
pen.right(90)
pen.forward(100) # Move forward by 100 units
pen.right(90)
pen.forward(100) # Move forward by 100 units
pen.right(90)
pen.forward(100) # Move forward by 100 units

screen.exitonclick()
 

• Download and run square2.py.txt. This is a version of square.py.txt that you can use as the basis of your HW assignment.
• Also, try to run it in IDLE by copying and pasting one statement at a time.

Explanations:

• "import turtle": import the built-in turtle module. This allows the program to use the turtle object.
• "pen = turtle.Turtle()" creates a turtle object and refers to it as "pen"
• "pen.forward(100)" moves the pen. Since the pen is down, the turtle also draws.
• "pen.right(90)" turns the turtle right 90 degrees.
• screen.exitonclick(): pause until the screen is clicked on to exit.