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Session 2: Telling the turtle what to do

Phase 2 — Python with Turtle · Session 2 of 8

What we’re learning today

Last week you typed your first Python code and made a turtle draw a square. Today we’ll learn more things the turtle can do — jump to specific spots, face specific directions, draw circles, and even write text. By the end, you’ll be able to draw a small scene with multiple parts: a sun, a house, a tree.

You’ll need to remember from last time

  • Open Thonny, type code in the editor, save with a .py extension, click Run (or press F5).
  • Every Python turtle program starts with import turtle and t = turtle.Turtle().
  • t.forward(N), t.right(N), t.left(N) for movement.
  • t.color("red") and t.pensize(N) for style.
  • t.penup() and t.pendown() for skipping without drawing.
  • Sequences run top to bottom. Order matters in Python just like it did in Scratch.

Part A: More ways to tell the turtle what to do

Open Thonny, start a new file, and save it as scene.py. Type the standard opening:

import turtle
t = turtle.Turtle()

You’ll add to it.

Jumping to a specific spot: goto

In Scratch, you used go to x: 0 y: 0 to send a sprite to a specific position. Python turtle has the same idea. The stage has a coordinate system: the middle is (0, 0), x goes right (positive) and left (negative), y goes up (positive) and down (negative).

Add this to your file:

t.penup()
t.goto(100, 50)
t.pendown()
t.forward(50)

Save. Run.

The turtle lifts its pen, jumps to the point (100, 50), drops the pen, and walks 50 forward from there.

You’ll use goto constantly when you have multiple things to draw at different positions. Lift the pen, jump, drop the pen, draw.

Facing a specific direction: setheading

After goto, your turtle is somewhere, but which way is it facing? It’s facing wherever it was facing before. That’s often not what you want.

setheading makes the turtle face a specific direction:

  • t.setheading(0) — face right (east)
  • t.setheading(90) — face up (north)
  • t.setheading(180) — face left (west)
  • t.setheading(270) — face down (south)

So if you want to draw something that points up, you do:

t.penup()
t.goto(0, 0)
t.setheading(90)   # face up
t.pendown()
t.forward(80)      # draw an upward line

Use goto and setheading together when you need to start drawing in a known place at a known angle. Most multi-part drawings need both.

Circles

The turtle can also draw circles. Add this:

t.penup()
t.goto(-150, 100)
t.pendown()
t.color("yellow")
t.pensize(3)
t.circle(40)

Save. Run. A yellow circle of radius 40 appears in the upper-left area.

t.circle(40) draws a complete circle. The circle starts where the turtle currently is, and the turtle ends up back at that same spot when the circle is done.

You can also draw a partial circle by giving a second argument — how many degrees of arc to draw. t.circle(40, 180) draws a half-circle.

Writing text

The turtle can write text too. Add:

t.penup()
t.goto(0, 150)
t.pendown()
t.color("black")
t.write("My Scene", font=("Arial", 20, "normal"))

Save. Run. The text “My Scene” appears at the top of your window.

The font=("Arial", 20, "normal") part says what font and size to use. Don’t worry about the syntax for now — just know you can change 20 to make the text bigger or smaller.

Build a scene together

Let’s combine everything into a small scene. Start fresh — delete your code and type this:

import turtle
t = turtle.Turtle()

# the sun
t.penup()
t.goto(150, 100)
t.pendown()
t.color("yellow")
t.pensize(2)
t.circle(30)

# the house body (a square)
t.penup()
t.goto(-50, -50)
t.setheading(0)
t.pendown()
t.color("brown")
t.pensize(3)
t.forward(100)
t.left(90)
t.forward(100)
t.left(90)
t.forward(100)
t.left(90)
t.forward(100)
t.left(90)

Save. Run.

You should see a yellow sun in the upper right and a brown square (house) below it.

Notice the lines starting with # — those are comments. Anything after a # on a line is ignored by Python. Comments are how you leave notes for yourself (or other readers) explaining what each part of your code does. We’ll use them more as our programs get bigger.

Checkpoint: You have a scene with at least two distinct elements (a sun and a house, or similar) drawn at different positions on the stage. This is the natural stop point if class is cut short.

Part B: Make it your scene

Now make this scene yours. The base goal is small; the stretch adds to it; the extension lets your imagination loose.

Base goal

Add a third element to your scene. Pick one:

  • A roof on top of the house. (Triangle. Use goto to position the turtle at one corner, setheading to face the right way, then three forward/left pairs to draw the triangle. Don’t forget the third turn at the end so the turtle’s heading is predictable for whatever comes next.)
  • A tree. A brown rectangle for the trunk, a green circle for the leaves on top.
  • A second sun of a different color, in another corner.
  • A title. Use t.write() to put your name or a title at the top of the scene.

Stretch

Add two more elements, of any kind. Mountains in the background. A second house. A road. A door on the existing house. Something that makes the scene feel like a place.

Start using comments (# something) to label what each part of your code is. It’ll help you find things when the program gets longer.

Extension

Tell a tiny visual story. Add elements that suggest something is happening — a second person/animal, a path, smoke from the house’s chimney, weather (clouds, rain, sun rays). Use as many turtle commands as you can.

Some commands you haven’t formally seen but might want:

  • t.circle(radius, extent) — partial circle
  • t.shape("turtle") — make the cursor look like a little turtle
  • t.speed(0) — turn the turtle drawing animation off (way faster)
  • t.hideturtle() — hide the cursor entirely after drawing

Try them. The “If you finish early, just try things and see what happens” energy is exactly the right mindset.

Wrap-up

Before we leave, share with the room:

  • What’s in your scene?
  • What was the trickiest part to position correctly?
  • Did anyone discover a turtle command we didn’t talk about?

You did something interesting today: you used multiple parts of your code to build one thing. The sun, the house, the tree — each a separate sequence of commands, all together making one drawing. That’s how every real program works. Big programs are made of small pieces, each doing one thing.

Your scene is also probably long now — maybe 40 or 50 lines. Some of those lines repeat. Like the four pairs of forward(100) / left(90) to draw the square. Wouldn’t it be great if you could say “draw a square” instead of typing those eight lines?

You can. That’s next week.

If you missed this session

Open Thonny and start a new file. Save it as scene.py. Then:

  1. Build the standard opening (import turtle and t = turtle.Turtle()).
  2. Practice with goto: t.penup(), t.goto(100, 50), t.pendown(), t.forward(50). Run and see the turtle jump.
  3. Practice with setheading: t.setheading(90), t.forward(50). The turtle now draws a line going up.
  4. Practice with circle: t.color("yellow"), t.circle(40). The turtle draws a yellow circle.
  5. Now build the scene from Part A above (sun + house). Then add one more element (Part B base).

About 30-40 minutes of work. If you get stuck, ask your buddy at the start of next class.

Stretch and extension ideas

  • Use t.fillcolor("red") and surround a shape with t.begin_fill() / t.end_fill() to fill it with color, not just outline.
  • Use t.bgcolor("skyblue") to set the background color of the whole window.
  • Use multiple turtles. After import turtle, do t = turtle.Turtle() and s = turtle.Turtle(). Now you have two turtles you can control independently. (Hint: this gets way more useful when we have loops next week.)

What’s next

Next week we finally get loops in Python. Remember when you typed eight lines to draw a square last week, and your house this week? Next week you’ll do it in three. By the end of class, you’ll be drawing patterns that would take hundreds of lines by hand.