What you’ll learn in this lesson

• What Turtle is, and why it comes free with Python
• How to move the turtle and turn it
• How to draw a square, then draw it with a loop
• How to change colors and lift the pen
• How to design a shape of your own

Meet the turtle

Turtle is a drawing tool built into Python itself — no download, no
install, it is already there. When you run a Turtle program, a drawing
window opens with a small arrow (the “turtle”) in the middle. Your
instructions move the turtle, and it draws a line wherever it walks.

Because Turtle is part of Python’s standard library, it works in IDLE
exactly like everything else in this course: write the program in a
file, run it, and watch the drawing window appear.

A note on this lesson’s code: Turtle draws pictures on screen, so its
programs cannot be run and checked on a machine with no screen the way
the other lessons’ code was. Every snippet below was checked for
correct syntax and uses only the standard Turtle commands listed in
this lesson — but you should run each one in IDLE yourself and watch
it draw, which is the whole point.

Moving and turning

Start with the two commands you will use most. forward() moves the
turtle ahead by a number of steps (think pixels on screen).
right() turns it clockwise by a number of degrees.

import turtle

t = turtle.Turtle()
t.forward(100)
t.right(90)
t.forward(100)

turtle.done()

Run this in IDLE. The turtle draws a line 100 steps long, turns right
by 90 degrees (a quarter turn), and draws a second line. Two lines, an
L shape.

Three things to understand in this snippet:

• import turtle loads the Turtle tool. Without it, Python has no
  idea what turtle means.
• t = turtle.Turtle() creates your turtle and stores it in the
  variable t. From now on, t.forward(...) means “my turtle, move
  forward.”
• turtle.done() at the end keeps the drawing window open so you can
  admire your work. Without it, the window may close at once.

backward() moves the turtle back the way it faces, and left()
turns it counter-clockwise. Those four moves — forward,
backward, right, left — are enough to draw anything made of
straight lines.

A square, then a square with a loop

Four lines and four quarter-turns make a square. Written out longhand:

import turtle

t = turtle.Turtle()
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)

turtle.done()

That works, but it repeats the same two lines four times — exactly the
problem loops were invented to solve in Lesson 9:

import turtle

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

turtle.done()

Same square, in a third of the lines. The loop says “do these two
moves four times.” This is the moment loops stop being abstract: you
can see why repeating without retyping matters.

Colors and lifting the pen

color() changes the pen’s color. penup() lifts the pen so the
turtle moves without drawing; pendown() puts it back down. Together
they let you draw in several colors without connecting lines:

import turtle

t = turtle.Turtle()
t.color("red")
for side in range(4):
    t.forward(100)
    t.right(90)
t.penup()
t.forward(150)
t.pendown()
t.color("blue")
t.circle(50)

turtle.done()

Run it: a red square, then the turtle silently moves 150 steps to the
side (pen up, no line), then draws a blue circle with circle(50),
which draws a circle of radius 50. Color names are plain English
words in quotes: "red", "blue", "green", "purple", "orange".
If you misspell one, Turtle will tell you — another friendly error
message, pointing at the exact problem.

Design a shape of your own

You now know enough to invent. A triangle is three sides and three
turns of 120 degrees (because 3 × 120 = 360, a full turn). A house is
a square plus a triangle roof. A star takes five sides and 144-degree
turns — try it and see why the angle is not the obvious one.

The habit to build here is the same one from every lesson: guess,
run, look at what actually happened, and adjust. With Turtle, the
feedback is a picture, which makes the guess-and-check loop feel like
play. That is not an accident — it is why Turtle has been a
beginner’s favorite for decades.

import turtle
t = turtle.Turtle()
t.forward(100)
t.right(90)
t.forward(100)
turtle.done()

Output: an L shape, drawn on screen.

import turtle
t = turtle.Turtle()
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
t.forward(100)
t.right(90)
turtle.done()

import turtle
t = turtle.Turtle()
for side in range(4):
    t.forward(100)
    t.right(90)
turtle.done()

Output: the same square, drawn on screen.

import turtle
t = turtle.Turtle()
t.color("red")
for side in range(4):
    t.forward(100)
    t.right(90)
t.penup()
t.forward(150)
t.pendown()
t.color("blue")
t.circle(50)
turtle.done()

Output: a red square and a blue circle, drawn on screen.

Download the Lesson 11 slides (PowerPoint, with narration)

Download the Lesson 11 slides (PDF)

Hands-on exercise

1. Draw a square with a loop, exactly like the lesson, and run it in
   IDLE.
2. Change the loop to draw a triangle (3 sides, 120-degree turns)
   and run it.
3. Draw two shapes in different colors, using penup() and
   pendown() to move between them without a connecting line.
4. Invent one shape of your own — a house, a star, or anything else
   — and write down how many sides and what turn angle it needed.

Press Run to draw.

Practice file

Save this as lesson11-practice.py and run it with F5 in IDLE.

# Lesson 11: Drawing with Turtle
# WHAT TO DO: Turtle is a drawing tool built into Python. This program
# draws a shape with a loop: go forward, turn right, repeat. A square
# needs 4 sides, but the loop below repeats only 3 times. Fix line 18:
# change range(3) to range(4).
# HINT: Each repeat draws one side and one 90-degree turn, so 4 repeats
# make a square. Only change the number 3.
# NOTE: On a computer with no screen, Turtle cannot open its drawing
# window, so the program prints a message instead of drawing. That is
# expected there — run it in IDLE on your own computer to see the square.
# Run with F5 in IDLE. You are done when the drawing is a closed square.

import turtle

try:
    t = turtle.Turtle()
    t.color("blue")
    for side in range(3):  # <-- CHANGE THIS LINE: a square has 4 sides
        t.forward(100)
        t.right(90)
    turtle.done()
except Exception:
    print("Turtle needs a screen to draw.")
    print("In IDLE, this program draws a square: 4 sides of 100 steps.")

Key takeaways

• Turtle is built into Python: import turtle, then t = turtle.Turtle().
• forward() and backward() move; right() and left() turn in degrees.
• A loop plus Turtle turns repetition into pictures you can see.
• color() changes pen color; penup()/pendown() control whether movement draws.
• circle(50) draws a circle of radius 50; turtle.done() keeps the window open.

Next lesson: Lists.

Quick quiz

1. What does import turtle do, and why is it needed?
2. What do t.forward(100) and t.right(90) do?
3. Why is the loop version of the square better than writing all eight lines out?
4. What do penup() and pendown() do?
5. What does turtle.done() do, and what happens without it?

Answer key: 1. It loads the Turtle tool; without it Python does not know what turtle means. 2. Move forward 100 steps; turn right 90 degrees. 3. It says the two moves once and repeats them four times, instead of retyping them. 4. penup() lifts the pen so movement draws nothing; pendown() puts it back down to draw again. 5. It keeps the drawing window open; without it the window may close at once.