What This Is

Everything you have written so far prints text. Turtle draws pictures instead. It comes with Python — nothing to install.

You control a pen that moves around a window. Tell it to go forward, turn, and change color, and it leaves a line behind it. That is the whole idea.

This pairs with Activity 1.16 For Loops on purpose. Drawing a square by hand takes eight lines. Drawing it with a loop takes three, and once you can loop, you can draw things that would be miserable to write out by hand.

Getting Started

Create a file named le-turtle and run this:

import turtle

turtle.forward(100)
turtle.right(90)
turtle.forward(100)

turtle.done()

A window should open and draw two lines meeting at a right angle. turtle.done() on the last line is what keeps the window from closing the instant the program ends — leave it off and you will see a flash of nothing.

If no window appears at all, turtle needs a piece of Python called tkinter, and some installations leave it out. Tell me and we will sort it out — it is not something you did wrong.

Work Through These

1. A square, with a loop

Four sides, four identical turns. That is a for loop wanting to happen.

import turtle

for side in range(4):
    turtle.forward(100)
    turtle.right(90)

turtle.done()

Note that side is never used inside the loop. That is fine — sometimes you only want the loop to repeat, not to count.

2. Color, width, and speed

import turtle

turtle.speed(0)
turtle.pencolor("cyan")
turtle.width(3)

for side in range(6):
    turtle.forward(120)
    turtle.right(60)

turtle.done()

turtle.speed(0) means "as fast as possible" — you will want it once your drawings get bigger. Try changing the 6 and the 60 together and see what shapes you get.

Here is the pattern worth knowing: for any regular shape, the turn is 360 divided by the number of sides. Six sides, 60 degrees. Eight sides, 45. Work out why.

3. A spiral

Now use the loop variable instead of ignoring it. Each pass draws a slightly longer line than the last.

import turtle

turtle.speed(0)

for step in range(90):
    turtle.forward(step * 3)
    turtle.right(89)

turtle.done()

Change the 89 to 90 and run it again. One degree of difference changes the whole picture — that is worth staring at for a moment.

Then Make Something

Draw something of your own. Ideas, in rough order of difficulty:

• A triangle, a hexagon, and an octagon side by side
• A five-pointed star — the turn is not 72 degrees, work it out
• A row of squares, using a loop inside a loop
• Your initials
• Ask the user how many sides they want, then draw that shape — now you are combining turtle with input() and casting

To submit: your .py file and a screenshot of what it drew.