Code-Along: Loopy Turtle

This activity shows how you can use loops to create some very interesting Turtle patterns in Python.

Click here for the starter project.

Part One: Understanding the Existing Code

There is already quite a bit of code in the project. So far, it:

Creates a turtle
Sets up the screen
Sets the turtle and background colors
Moves the turtle without drawing (using penup)
Starts a fill
Draws a small triangle based on a loop that runs 2 times

This code doesn't do much, but it lays the groundwork for something much more interesting.

Part Two: Updating the Loop

Fix the for loop code so that instead of drawing a triangle with width 40, it draws a square with width 400.

Make the loop run 4 times instead of 2
Make the turtle move forward 400 pixels instead of 40

The updated for loop code should look something like this:

for x in range(4):
  keisha.forward(400)
  keisha.right(90)

Part Three: A New Pattern

Now there should be a nice blue square: a perfect canvas upon which to bestow a lovely geometric design. This will consist of a few different steps.

Step A: Position the Turtle

First, change the turtle's color and position it appropriately.

Set the color to white
Pick up the pen
Move to coordinates of (0, -100)
Put the pen back down

After these commands, the turtle should be ready to draw. The code should look something like this:

keisha.color("white")

keisha.penup()
keisha.goto(0, -100)
keisha.pendown()

Step B: Setup the Loop

Now it's time for a totally new loop. This should look a lot like the other loop, but it will do some different things. First, make a new line at the bottom of the main.py file. Then:

Add the basic for loop structure code to loop 36 times
- for
- x
- in
- range
- Parentheses ()
- Number 36
- Colon :
Make a new line
Indent the new line by hitting Space twice
Make the turtle draw a circle with radius 40

Once the new for loop is in place, run the project again. It should be looping... for now, it's just doing the same thing over and over again, but that's a good start.

The code should look something like this:

for x in range(36):
  keisha.circle(40)

Step C: Move Forward

The next step is to move the turtle along with each time through the loop. This will layer each circle in an interesting way, instead of simply drawing all the circles right on top of each other.

Make a new line at the bottom of the file
Indent the new line by hitting Space twice
- Note: It should be at the same indentation level as the keisha.circle command
Move the turtle forward 20 pixels

Run the code again, and see how it gets a little more interesting! Now the turtle draws different circles veering off to the right.

The code should look something like this:

for x in range(36):
  keisha.circle(40)
  keisha.forward(20)

Step D: Complete the Cycle

It looks pretty cool, but what we really want is to make a donut. This will be possible by adding one more command to run every time through the loop.

Make a new line at the bottom of the file
Indent the new line by hitting Space twice
- Note: It should be at the same indentation level as the keisha.circle command
Turn the turtle to the left 10 pixels

Run the code again - now, the turtle should be making a pretty cool cyclical pattern.

Conclusion

And that's it! The code at the end of the activity should look something like this:

from turtle import *

keisha = Turtle()
paper = keisha.getscreen()
paper.setup(500, 500)

keisha.color("blue")
paper.bgcolor("white")

keisha.penup()
keisha.goto(-200, 200)
keisha.pendown()

keisha.begin_fill()

for x in range(4):
  keisha.forward(400)
  keisha.right(90)

keisha.end_fill()

keisha.color("white")

keisha.penup()
keisha.goto(0, -100)
keisha.pendown()

for x in range(36):
  keisha.circle(40)
  keisha.forward(20)
  keisha.left(10)

Code-Along