Lesson 2: Introducing Turtle¶

In this lesson we will learn

how to import a module into our program
how to create a turtle and set up its window
how to move and turn the turtle to draw lines
how to draw simple shapes like squares and triangles

Terminology

module – an extra group of commands that we can add to our program.
import – the command that tells Python to load a module so our program can use its commands.
turtle – a small arrow on the screen that we can control and move around to draw.
screen – the window that the turtle draws in.
pixel – one of the tiny dots that make up a screen, also used to measure how far the turtle moves.

Our first turtle program¶

Create a new file, type in the comment below, and save it as first_turtle.py.

1	`# Our first turtle program`

Python starts with a small set of built-in commands called functions. It can also use extra groups of commands called modules. One of these modules is turtle.

To use a module, we need to tell Python with the import command. We always put import lines at the very top of our program.

Add line 3 so our code looks like this:

# Our first turtle program

import turtle

PRIMM

Predict what you think will happen when we run the code.
Run the code. Did anything appear?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module so our program can use its commands.

Nothing appears yet. Importing a module only makes its commands available. We haven't used any of them yet.

Create a turtle¶

A turtle is a small arrow on the screen that we can control and move around. Before we can use a turtle, we need to create one.

Add line 5 so our code looks like this:

# Our first turtle program

import turtle

my_ttl = turtle.Turtle()

PRIMM

Predict what you think will happen when we run the code.
Run the code. Did a window appear?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module.
line 5 → uses the Turtle() command from the turtle module to create a turtle, and names it my_ttl.

We can choose any name we like for our turtle. The name my_ttl is just an example. There are two rules:

the name must be one word, with no spaces
if we change the name, we must use the same name everywhere in our code

Make our turtle move¶

Now let's make the turtle move. Add line 7 so our code looks like this:

# Our first turtle program

import turtle

my_ttl = turtle.Turtle()

my_ttl.forward(100)

PRIMM

Predict what the turtle will do. Be specific.
Run the code. You might have guessed the turtle would move to the right, but did you expect it to leave a line behind it?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module.
line 5 → creates a turtle called my_ttl.
line 7 → tells my_ttl to move forward 100 steps, drawing a line as it goes.

PRIMM

Time to modify the code. Can you make the turtle draw lines of different lengths?

Changing the turtle window¶

Let's set up the turtle window so it looks the same on every computer. Change our code so it matches the code below. Lines 5 and 6 are new.

# Our first turtle program

import turtle

window = turtle.Screen()
window.setup(500, 500)

my_ttl = turtle.Turtle()

my_ttl.forward(100)

PRIMM

Predict what will change when we run the code.
Run the code. Did the window change?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module.
line 5 → uses the Screen() command from the turtle module to create the window, and names it window.
line 6 → sets the window to 500 pixels wide and 500 pixels high.
line 8 → creates a turtle called my_ttl.
line 10 → moves my_ttl forward 100 steps.

In the turtle module, the window is called a screen. We create a screen the same way we created a turtle.

What are pixels?

Our screen is made up of lots of tiny dots. If you look very closely, you might be able to see them. These dots are called pixels.

You might see screen sizes written like 1920 × 1080. This means the screen is 1,920 pixels wide and 1,080 pixels high.

Pixels are also how the turtle measures movement. When we write forward(100), the turtle moves forward 100 pixels.

Changing the turtle's shape¶

Now let's change how the turtle looks. Add line 9 to our program.

# Our first turtle program

import turtle

window = turtle.Screen()
window.setup(500, 500)

my_ttl = turtle.Turtle()
my_ttl.shape("turtle")

my_ttl.forward(100)

PRIMM

Predict what this change will do.
Run the code. Was your guess correct?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module.
lines 5–6 → create a 500 × 500 pixel window.
line 8 → creates a turtle called my_ttl.
line 9 → changes my_ttl from an arrow into a turtle shape.
line 11 → moves my_ttl forward 100 steps.

Change direction¶

Now that our window and turtle are ready, let's do more drawing. Add lines 12 and 13 to the bottom of our code.

# Our first turtle program

import turtle

window = turtle.Screen()
window.setup(500, 500)

my_ttl = turtle.Turtle()
my_ttl.shape("turtle")

my_ttl.forward(100)
my_ttl.left(90)
my_ttl.forward(100)

PRIMM

Predict what this code will do. Be as specific as you can, and draw what you think will happen on a piece of paper.
Run the code. Did the turtle draw the same thing as your picture?
Time to investigate the code. What does each line do?

Code explanation

line 3 → imports the turtle module.
lines 5–6 → create a 500 × 500 pixel window.
lines 8–9 → create a turtle called my_ttl with a turtle shape.
line 11 → moves my_ttl forward 100 steps.
line 12 → turns my_ttl 90 degrees to the left.
line 13 → moves my_ttl forward another 100 steps.

PRIMM

Time to modify the code. What happens when we change the numbers inside the brackets? Can you make the turtle turn right using right()?

Exercises¶

In this course, the exercises are the make part of PRIMM. Work through them to make your own code.

Starter files are in the lesson_02 folder of the tutorial files. Solutions are on the Exercise Solutions page.

Exercise 1¶

Starter: lesson_02/ex1_square

Can you add code to the end of the starter so the turtle draws a square?

Exercise 2¶

Starter: lesson_02/ex2_triangle

Can you add code to the end of the starter so the turtle draws an equilateral triangle (a triangle with three equal sides)?

Exercise 3¶

Starter: lesson_02/ex3_hexagon

Can you add code to the end of the starter so the turtle draws a hexagon (a shape with six equal sides)?