17. Turtle

Turtle is part of the Python API used to draw graphics on the screen. The main objects in Turtle are the Screen and Pen. The Screen is the canvas that is being drawn onto and the Pen is the object that you use to draw. As always, the best way to learn Turtle is to see some examples and start coding your own creations.

17.1. Draw a line

Here’s a simple program to draw a square.

import turtle

# w is an instance of Screen
# we choose w as the variable name to denote `window`
# we will use the terms `screen` and `window` interchangeably
w = turtle.Screen()

# let's set a title for the window
w.title('Line')

# t is an instance of Turtle
# a Turtle is also known as a `pen`
t = turtle.Turtle()

# draw a line
t.forward(50)

# starts the event loop
# the event loop listens for events
turtle.done()

Line output.

17.2. Draw a square

Here’s a simple program to draw a square.

import turtle

# w is an instance of Screen
# we choose w as the variable name to denote `window`
# we will use the terms `screen` and `window` interchangeably
w = turtle.Screen()

# let's set a title for the window
w.title('Square')

# t is an instance of Turtle
# a Turtle is also known as a `pen`
t = turtle.Turtle()

# we will loop 4 times
# each time, we make the turtle move forward and turn right 90 degrees
for i in range(4):
    t.forward(50)
    t.right(90)

# starts the event loop
# the event loop listens for events
turtle.done()

Square output.

17.3. Draw stars

Here’s code to draw a star.

import turtle

w = turtle.Screen()
w.title('Star')

t = turtle.Turtle()

for i in range(5):
    t.forward(50)
    t.right(144)

turtle.done()

Star output.

Let’s draw a fancy star.

import turtle

w = turtle.Screen()
w.title('Fancy Star')

t = turtle.Turtle()

for i in range(20):
    t.forward(i * 10)
    t.right(144)

turtle.done()

Star output.

17.4. Draw rectangular spirals

Let’s draw a rectangular spiral from the inside out. We will change the color that the turtle will use to red. We will also define the spiral function to draw each spiral.

import turtle

def spiral(size, t, delta=-5):
    for i in range(4):
        t.fd(size)
        t.left(90)
        size = size + delta

w = turtle.Screen()
w.title('Inside Out')

t = turtle.Turtle()
t.color('red')
nums = list(range(6, 147, 20))

for num in nums:
    spiral(num, t, delta=5)

turtle.done()

Inside-out rectangular spiral output.

Let’s draw a rectangular spiral from the outside-in. Since we are drawing the spirals from the outside-in, we will reverse the sizes.

import turtle

def spiral(size, t, delta=-5):
    for i in range(4):
        t.fd(size)
        t.left(90)
        size = size + delta

w = turtle.Screen()
w.title('Outside In')

t = turtle.Turtle()

t.color('blue')
nums = list(range(26, 147, 20))
nums.reverse()

for num in nums:
    spiral(num, t)

turtle.done()

Outside-in rectangular spiral output.

17.5. Draw polygons

How about polygons? Let’s draw a hexagon.

import turtle

w = turtle.Screen()
w.title('Hexagon')

t = turtle.Turtle()

n_sides = 6
s_len = 70
angle = 360.0 / n_sides

for i in range(n_sides):
    t.forward(s_len)
    t.right(angle)

turtle.done()

Hexagon output.

17.6. Draw a spiral helix

Let’s draw a spiral helix. First, let’s change the background color to black. Second, let’s define the colors that we want the pen to use. Lastly, since there’s a lot to draw, let’s set the speed of the pen to 100.

import turtle

w = turtle.Screen()
w.title('Spiral Helix')
w.bgcolor('black') 

colors = ['red', 'purple', 'blue', 'green', 'orange', 'yellow']

t = turtle.Pen() 
t.speed(100)

for x in range(360): 
    color = colors[x % len(colors)]
    t.pencolor(color) 
    t.width(x / 100 + 1) 
    t.forward(x) 
    t.left(59) 

turtle.done()

Spiral helix output.

17.7. Dots

Here’s an exercise in drawing dots. We use penup to make sure no drawing is done when moving and dot to place the pen down to create the dots. Additionally, if you want the change the shape of the pen from a classic arrow, you may use the shape method. Below, for each row of dot we are drawing, we change the shape.

import turtle

t = turtle.Turtle()

dot_distance = 25
width = 5
height = 7

shapes = ['arrow', 'circle', 'classic', 'square', 'triangle', 'turtle']

t.penup()

for y in range(height):
    shape = shapes[y % len(shapes)]
    
    t.shape(shape)

    for i in range(width):
        t.dot()
        t.forward(dot_distance)
    t.backward(dot_distance * width)
    t.right(90)
    t.forward(dot_distance)
    t.left(90)
    
turtle.done()

Dots output.

We may also stamp out colorful patterns.

import turtle

t = turtle.Turtle()

dot_distance = 25
width = 5
height = 7

shapes = ['arrow', 'circle', 'classic', 'square', 'triangle', 'turtle']
colors = ['red', 'purple', 'blue', 'green', 'orange', 'yellow']

t.penup()

for y in range(height):
    shape = shapes[y % len(shapes)]
    color = colors[y % len(colors)]

    t.shape(shape)
    t.pencolor(color)
    t.color(color)

    for i in range(width):
        t.stamp()
        t.forward(dot_distance)
    t.backward(dot_distance * width)
    t.right(90)
    t.forward(dot_distance)
    t.left(90)
    
turtle.done()

Stamp output.

17.8. Crazy lines

Let’s draw some crazy lines. We use penup and pendown to control when we want the pen to draw onto the canvas. Note that as we iterate through the angles, we speed up the pen’s drawing speed as well as change its colors.

import turtle 

t = turtle.Turtle()

colors = ['red', 'purple', 'blue', 'green', 'orange', 'yellow']
speed = 10

for i in range(180):
    color = colors[i % 6]

    t.pencolor(color)
    t.speed(speed)

    t.forward(100)
    t.right(30)
    t.forward(20)
    t.left(60)
    t.forward(50)
    t.right(30)
    
    t.penup()
    t.setposition(0, 0)
    t.pendown()
    
    t.right(2)

    speed = speed + 2
    
turtle.done()

Crazy lines output.

17.9. Bright sun

Here’s a sun. Notice how we change the import statement from import turtle to from turtle import *? Now we have access to the begin_fill and end_fill methods, which fills up the shape we draw where we mark begin and end.

from turtle import *

speed(50)
color('red', 'yellow')

begin_fill()

while True:
    forward(200)
    left(170)
    if abs(pos()) < 1:
        break

end_fill()

done()

Sun output.

17.10. Events

We may also interact with the turtle through listening for events. In this example, we listen for key events using the screen’s onkey function and call listen after we have defined all the keys we are listening to. When a user presses

• the up arrow, we move up

• the down arrow, we move down

• the left arrow, we move left

• the right arrow, we move right

• the p key, we toggle the pen up and down state

• the q key, we quit the program

We use the pen’s setheading to orient the cursor as appropriate (to the north, south, east or west) before we move.

import turtle

def up():
    t.setheading(90)
    t.forward(50)
    state = 'up'
    print(state)

def down():
    t.setheading(270)
    t.forward(50)
    state = 'down'
    print(state)
    

def right():
    t.setheading(0)
    t.forward(50)
    state = 'right'
    print(state)

def left():
    t.setheading(180)
    t.forward(50)
    state = 'left'
    print(state)

def toggle_pen_up_down():
    if t.isdown():
        t.penup()
        print('pen up')
    else:
        t.pendown()
        print('pen down')

def close():
    print('close')
    turtle.bye()

w = turtle.Screen()
w.title('Event Listening')

t = turtle.Turtle()
p_state = 'down'

w.onkey(up, 'Up')
w.onkey(down, 'Down')
w.onkey(right, 'Right')
w.onkey(left, 'Left')
w.onkey(close, 'q')
w.onkey(toggle_pen_up_down, 'p')

w.listen()

turtle.done()

Event output.

17.11. Built-in examples

For even more examples, type in the following.

python -m turtledemo