Turtle Code-Along

In this introductory activity, use turtle graphics to create a drawing in Python!

Getting Started

Setup using Replit is fairly simple.

  1. Go to the TurtleStart Replit project
  2. Fork the project, and make sure to log in!
  3. In the code section, add the following line to import everything from the turtle library:
     from turtle import *
  4. Click the green Run button, and notice that nothing happens yet
  5. Make a new line under the import, and add the following code:
     shelly = Turtle()
  6. shelly is now a Turtle object - but Shelly needs a shape! Under that line, add the following code to give Shelly a shape: 
     shelly.shape("arrow")
  7. Run the code again to see Shelly appear on the screen!
  8. BONUS: Update the code so that instead of an "arrow" shape, the turtle looks like a turtle

Code

from turtle import *

shelly = Turtle()
shelly.shape("arrow")

Adding Color

Make things a little more interesting by updating the colors.

  1. Make a new line, and add code to change Shelly's color
    • HINT: this is a lot like how the shape was updated - just using color instead
  2. On the next line, add the following code:
     paper = shelly.getscreen()
  3. Now, the paper variable stores the screen. Change its color using bgcolor
  4. BONUS: Play around with the settings to create a pleasing (or terrible) color scheme!

Code

shelly.color("maroon")
paper = shelly.getscreen()
paper.bgcolor("gold")

More Colors

Although there are many built-in colors, sometimes it is necessary to find a very specific color. In addition to using color names (like "red", "orange", etc), turtles can take color values in RGB format! The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. Basically, it is possible to create any digital color with a combination of red, green, and blue!

Each color (R, G, and B) can take a number from 0 to 255. This represents the amount of the color in the mix. For example, a color with a Red value of 255, a Green value of 0, and a Blue value of 0 would be red.

Try to guess how the following colors would look:

  • Red 255, Green 0, Blue 255
  • Red 255, Green 255, Blue 0
  • Red 0, Green 0, Blue 255
  • Red 255, Green 255, Blue 255
  • Red 0, Green 0, Blue 0
  • Red 255, Green 128, Blue 0

The combinations are almost endless! Google has a built-in color picker that developers and designers can utilize to find the perfect color. It displays RGB colors in this format:

rgb(92, 144, 66)

To translate that into Python code, do the following:

shelly.color(92, 144, 66)

This will set the color of the turtle to a dark green. The RGB method allows for much more specific colors, so developers can use precisely the color they need!

Moving the Turtle

One of the most useful turtle abilities is the ability to move across the screen and draw like a pen! Create a blank line, and then add the following command on the next line:

shelly.forward(50)

Click the Run button to see the turtle move across the screen! Specifically, it moves forward 50 pixels in the direction it is currently facing (90 degrees).

It is also possible to turn the turtle. Add the following command on the next line:

shelly.right(90)

This command turns the turtle 90 degrees to the right. Previously the direction of the turtle was 90 degrees (pointing to the right), so after turning 90 degrees to the right, the turtle should face down (180 degrees).

Run the program again to see the turtle move to the right, then turn to face down!

Drawing a Square

Add the following commands to the file, under the existing commands:

shelly.forward(50)
shelly.right(90)
shelly.forward(50)
shelly.right(90)

Run the program to see what this code does. It should draw part of a square! How does that work? On a piece of paper, or on a whiteboard, try to draw the same square as the turtle:

  1. Draw the top side from left to right
  2. Turn the writing utensil and draw the right side from top to bottom
  3. Turn the writing utensil and draw the bottom side from left to right

So, the turtle moves 50 pixels to the right, turns 90 degrees to face down, moves 50 pixels down, turns 90 degrees to face left, moves 50 pixels to the left, and then turns 90 degrees to face up!

BONUS

Try to complete the square that Shelly is drawing.

Another Turtle

Under the existing code, add code to make a new turtle:

crush = Turtle()
crush.shape("turtle")
crush.color("white")

This new turtle will be completely separate from the other one. Instead of drawing a square, it will draw a circle.

Add the following code to draw a half circle:

crush.circle(50, 180)

In the example, the radius of the circle will be 50, and it will complete a 180 degree rotation.

BONUS: instead of a half circle, draw a full circle!

A New Starting Point

Currently, the two turtles are kind of on top of each other. Fix this by adding a new starting point for the crush turtle.

Before the commands that make crush draw the circle, add the following command:

crush.setpos(-100, 100)

Run the program to see what happens. Crush moves, but there is another issue now!

Removing the Extra Pen Marks

When Crush moves to the starting point, the pen draws an extra line! Instead of doing this, the program should lift up the pen before this movement.

When working with turtles, it is possible to control whether the pen is "up" or "down" (like real life drawing). Before the crush.setpos command, add the following command:

crush.penup()

This will allow Crush to move without drawing anything! Run the program to see what happens.

Putting the Pen Back Down

Oh no! After lifting up the pen, Crush no longer draws the triangle! Fix this by adding the following command after the crush.setpos command:

crush.pendown()

This way, Crush will pick up the pen when moving to the starting point, and then put it back down before moving in the triangular fashion. Run the program again to see it work properly!

Other Possibilities

This only scratches the surface of turtle graphics capabilities. Try to play around with these commands, and check out the documentation to see what else is possible!

Final Code

from turtle import *

shelly = Turtle()
shelly.shape("arrow")

shelly.color("gold")
paper = shelly.getscreen()
paper.bgcolor("maroon")

shelly.forward(50)
shelly.right(90)
shelly.forward(50)
shelly.right(90)
shelly.forward(50)
shelly.right(90)
shelly.forward(50)
shelly.right(90)

crush = Turtle()
crush.shape("turtle")
crush.color("white")

crush.penup()
crush.setpos(-100, 100)
crush.pendown()

crush.circle(50, 180)

Challenges

After the activity, start working on the Turtle Challenges.

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