Compute with Turtles¶
A turtle here is not an animal. We are working with a virtual turtle, an idea that dates back to the 1960’s. The original robot turtle had a physical pen in it. The student-programmers would steer the robot around using programs, and create drawings with the pen.
Figure 3: Children playing with a Logo turtle robot that could draw with a pen
Today, we can play with virtual turtles in a fully-graphical and non-robotic
way. Below is a Python program that first reads in a library that contains
the code to let us work with turtles (from turtle import *). Then it
creates a Screen, a space for the turtle to move in and draw on
(space = Screen()). Next it creates a turtle named alex
(alex = Turtle()), then has alex move around on the space
(alex.forward(150)) and when it moves it will draw. The part of any line
that starts with a # character is called a comment. Python and the
computer ignores everything from the # character to the end of the line.
Comments explain what we’re doing in the programs and are intended to be
read by people, not computers.
Try clicking the 
button below to see what the following program
does.
Note
Notice that we tell alex what to do in the code above using dot
notation: alex.forward(150), alex.left(90), and
alex.forward(75). That is how you communicate with a turtle. You use
the name of the turtle followed by a . and then what you want it to do.
Note
If you are running this program on your computer, the screen will quickly
disappear after alex finishes his last command. Adding:
input() # wait for user to press the Enter key
at line 7 will pause the screen until the Enter key is pressed in the
active code window.
- North
- Check which way alex moved first.
- West
- Check which way alex moved first.
- South
- Check which way alex moved first.
- East
- Yes. Turtles start off facing east by default.
csp-1-5-1: Which direction will alex move when the code below executes?
from turtle import *
space = Screen()
alex = Turtle()
alex.forward(100)
Just by going forward, backward, left, and right, we can have a turtle draw a shape.
What shape will the program below draw when you click on the Run button?