Python Turtle Graphics

What is turtle graphics?

Turtle graphics is a way to draw pictures with code. You control a little turtle that carries a pen. When the turtle moves, it draws a line behind it — like dragging a marker across paper. Tell the turtle where to go, and it paints a picture for you.

It is built right into Python, so there is nothing extra to install. It is also one of the most fun ways to practice loops, functions and angles, because every command shows up instantly as a line on the screen.

Your first turtle

Every turtle program starts the same way: import the module and create a turtle.

import turtle

t = turtle.Turtle()

t.forward(100)

turtle.done()

Let's read it line by line:

• import turtle brings in the drawing tools.
• t = turtle.Turtle() creates a turtle and stores it in the variable t.
• t.forward(100) moves the turtle 100 steps forward, drawing a line.
• turtle.done() keeps the window open so you can see your art.

Run it and you'll see a short horizontal line. That line is your turtle's path.

Moving and steering

The turtle understands a small set of commands. These four are the most important:

Command	What it does
t.forward(d)	move forward d steps
t.backward(d)	move backward d steps
t.left(a)	turn left a degrees
t.right(a)	turn right a degrees

Notice that turning does not move the turtle — it only changes the direction it faces. You move with forward, and you steer with left and right. Combine them to go anywhere.

A worked example: drawing a square

Let's draw a square step by step. A square is four equal sides with a 90-degree turn at each corner.

import turtle

t = turtle.Turtle()

t.forward(100)   # bottom side
t.left(90)       # turn to face up
t.forward(100)   # right side
t.left(90)       # turn to face left
t.forward(100)   # top side
t.left(90)       # turn to face down
t.forward(100)   # left side
t.left(90)       # back to the start direction

turtle.done()

Trace it in your head: the turtle draws a line, turns left a quarter-turn, draws again, and repeats four times. After four turns of 90 degrees, it has turned a full 360 degrees and is back where it started, facing the way it began. The result is a neat square.

Use a loop to remove repetition

Look at the square code again. The pair of lines forward(100) and left(90) appears four times. Whenever you repeat the same steps, reach for a loop. (For a refresher, see Loops and Repeats.)

import turtle

t = turtle.Turtle()

for side in range(4):
    t.forward(100)
    t.left(90)

turtle.done()

This draws the exact same square, but the drawing instructions appear only once. The for side in range(4) line means "do the indented block 4 times." Shorter, clearer, and easier to change.

From squares to any polygon

Here is a beautiful trick. To draw any regular polygon, the turn angle is always 360 divided by the number of sides. A triangle turns 120 degrees (360 / 3), a pentagon turns 72 degrees (360 / 5), and so on.

import turtle

t = turtle.Turtle()

sides = 6          # change this to draw any shape
angle = 360 / sides

for side in range(sides):
    t.forward(100)
    t.left(angle)

turtle.done()

Change sides to 3 for a triangle, 5 for a pentagon, 8 for an octagon. One small change, a whole new shape. This is the power of letting the computer do the math.

Lifting the pen

Sometimes you want to move the turtle without drawing — for example, to start a new shape somewhere else. Use penup() to lift the pen and pendown() to put it back:

import turtle

t = turtle.Turtle()

# first square
for side in range(4):
    t.forward(60)
    t.left(90)

# move without drawing
t.penup()
t.forward(120)
t.pendown()

# second square
for side in range(4):
    t.forward(60)
    t.left(90)

turtle.done()

The penup() / pendown() pair leaves a gap between the two squares instead of a connecting line.

Wrapping drawings in a function

When you have a drawing you'll reuse, put it in a function so you can call it by name. (See Python Functions and Parameters for the full idea.)

import turtle

t = turtle.Turtle()

def draw_polygon(sides, length):
    angle = 360 / sides
    for side in range(sides):
        t.forward(length)
        t.left(angle)

draw_polygon(3, 80)    # triangle
t.penup(); t.forward(150); t.pendown()
draw_polygon(6, 80)    # hexagon

turtle.done()

Now draw_polygon is a reusable tool. Give it a number of sides and a length, and it draws that shape. The two inputs (sides and length) are parameters — they let one function draw many different shapes.

Making a spiral pattern

Now for something that looks impressive. If you draw lines while slowly turning and growing the length, you get a spiral:

import turtle

t = turtle.Turtle()
t.speed(0)        # fastest drawing

for step in range(120):
    t.forward(step)   # each line is a little longer
    t.left(59)        # turn by 59 degrees

turtle.done()

Each time through the loop the line is one step longer (forward(step)) and the turtle turns 59 degrees. Because 59 doesn't divide evenly into 360, the lines never line up, and a hypnotic spiral appears. Try changing 59 to 90, 91, or 144 and watch how the whole pattern transforms.

Try it yourself

1. Star: Draw a five-pointed star. Hint: loop 5 times, forward(150) then left(144) each time.
2. Colorful shapes: Add t.color("blue") before drawing, and try t.fillcolor("yellow"), t.begin_fill() ... t.end_fill() to fill a shape.
3. Pattern challenge: Use a loop inside a loop (a nested loop) to draw a square, turn a little, draw another square, and repeat — making a flower of overlapping squares.

import turtle

t = turtle.Turtle()
t.speed(0)

for turn in range(12):          # 12 squares around a circle
    for side in range(4):       # draw one square
        t.forward(100)
        t.left(90)
    t.left(30)                  # rotate before the next square

turtle.done()

Run that last one — it's a stunning pattern from just a few lines. Once you're comfortable, try combining turtle with what you learn in Making Decisions with If to draw different shapes based on a choice. Happy drawing!