Let’s make a turtle move around the screen, by running this short Python program:

from turtle import *
shape("turtle")
speed(5)

forward(100)
right(90)
forward(100)

done()

The turtle has a pen attached, and draws a line as it moves around the screen. Here’s what the program does:

• from turtle import * tells Python that you want to use the turtle library, a collection of code you can use to draw on the screen. The * means ‘import everything’.

• shape("turtle") makes the drawing robot look like a turtle. As well as turtle, you can also use “arrow”, “circle”, “square”, “triangle” or “classic”.

• speed(5) tells the turtle how fast to draw. You can use a number between 1 and 11. 11 is the fastest, 1 is the slowest.

• forward(100) and backward(100) tells the turtle to move forward or backward 100 pixels.

• left(45) and right(90) turn the turtle left or right by a number of degrees. Here are some examples:

  

• done() tells Python that we’ve finished programming the turtle.

What’s your favourite colour? To make your drawings more interesting, you can also change the colour and the size of the pen drawing the line. Here’s a simple example to try:

from turtle import *
shape("turtle")
speed(8)

color("Purple")
pensize(7)
right(90)
forward(100)
left(90)
forward(50)

color("Orange")
pensize(3)
penup()
forward(50)
pendown()
forward(50)

done()

The code above contains a couple of new commands:

• color("Purple") turns the turtle and the line purple. Notice the American spelling of the word colour, which doesn’t have a ‘u’ in it. You can also specify colours in hex, like you did in CSS. Instead of using pencolor("Red") you could use pencolor("#FF0000").

• penup() lifts the pen from the screen, and pendown() lowers it again. This means that you can move the turtle without leaving a trail!

Open up a new file, and run the following program:

from turtle import *

speed(11)
shape("turtle")

for count in range(4):
    forward(100)
    right(90)

done()

This program uses a for loop. You can use a for loop in Python whenever you want to repeat some code a set number of times.

In the program above, the commands forward(100) and right(90) are repeated 4 times, drawing a square. Turning 90 degrees for each corner means we turn 360 degrees in total.

Just like with an if statement, you should use the Tab key to indent the code that you want to repeat. Try changing the code, so that the line forward(100) is indented but the line right(50) isn’t, like this:

from turtle import *

speed(11)
shape("turtle")

for count in range(4):
    forward(100)
right(90)

done()

What happens when you run this program? Did you get a straight line? In this program, Python will repeat forward(100) four times, and then turn right(90).

Now that you know how to repeat commands, you can create complicated shapes and patterns really easily. Run this program:

from turtle import *

speed(11)
shape("turtle")

for count in range(8):
    forward(100)
    right(45)

done()

This program works in the same way as the square drawing program, except that it repeats 8 times, and only turns 45 degrees for each corner. This means that the code draws an 8-sided shape (an octagon), as the corners for each of the 8 sides add up to 360 degrees (360 divided by 8 is 45).

Here’s another example of what can be created using a for loop. What does this program draw?

from turtle import *

speed(11)
shape("turtle")

for count in range(30):
    forward(5)
    penup()
    forward(5)
    pendown()

done()