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17.10. Creating Functions with Turtles

Learning Objectives:

• Create functions that take a turtle object and draw a shape

• Add parameters to make functions more reusable

• Use begin_fill and end_fill to fill a shape

• Use bgcolor on the screen to change the background color of the screen object.

Here is code that draws a square with a turtle using a for loop with range.

Run the code to see what it draws.

from turtle import * # use the turtle library space = Screen() # create a turtle space alisha = Turtle() # create a turtle named alisha alisha.setheading(90) # point due north for sides in range(4): # repeat the indented lines 4 times alisha.forward(100) # move forward by 100 units alisha.right(90) # turn by 90 degrees

We can create a function out of the code that draws the square.

• Keep the import at the top of the code

• Move the code that draws the square after the import

• Add a function definition and pass in a turtle object. You can call it anything, but turtle is a good name for an object of the Turtle class.

• Modify the code in the function to use the local name (turtle).

• Add a call to the function after you create the turtle and pass in the turtle object. Use whatever name you gave the turtle when you created it.

When we execute square(alisha) the local variable turtle is set to the same object as alisha. Notice that we still need to import the library, create the screen object, create the turtle object, and call the function.

Run the code to see what it draws.

from turtle import * # use the turtle library def square(turtle): turtle.setheading(0) # set the heading to east for sides in range(4): # repeat the indented lines 4 times turtle.forward(100) # move forward by 100 units turtle.right(90) # turn by 90 degrees space = Screen() # create a turtle space alisha = Turtle() # create a turtle named alisha square(alisha) # call the square function

We can change the square function to take a length to make it more reusable. We can change the length when we call the function to draw different squares. We can even set a default value for length in case a value isn’t specified for it.

Run the code to see what it draws.

from turtle import * # use the turtle library def square(turtle, length = 100): turtle.setheading(0) # set the heading to east for sides in range(4): # repeat the indented lines 4 times turtle.forward(length) # move forward by 100 units turtle.right(90) # turn by 90 degrees space = Screen() # create a turtle space alisha = Turtle() # create a turtle named alisha square(alisha, 20) # call the square function alisha.penup() # pick up the pen alisha.goto(40,0) # move to (40, 0) alisha.pendown() # put down the pen square(alisha,40) # draw another square alisha.penup() # pick up the pen alisha.goto(-100,0) # move to (-100, 0) alisha.pendown() # put down the pen square(alisha) # draw another square

Let’s practice creating reusable functions from code that draws a shape with a turtle object.

Run the code first to see what it draws and then modify it to create a triangle function and pass in the length of each side. Then draw several triangles with the function.

from turtle import * # use the turtle library space = Screen() # create a turtle space alisha = Turtle() # create a turtle named alisha alisha.setheading(60) # set the heading for sides in range(3): # repeat the indented lines 3 times alisha.forward(100) # move forward by 100 units alisha.right(120) # turn by 120 degrees

We can add even more parameters to set the fill color. We can make the default fill color green. Use begin_fill() to start the shape you want to fill and end_fill() after the shape is finished.

Run the code to see what it draws.

from turtle import * # use the turtle library def square(turtle, length = 100, color = 'green'): turtle.setheading(0) # set the heading to east turtle.fillcolor(color) turtle.begin_fill() for sides in range(4): # repeat the indented lines 4 times turtle.forward(length) # move forward by length turtle.right(90) # turn by 90 degrees turtle.end_fill() space = Screen() # create a turtle space alisha = Turtle() # create a turtle named alisha square(alisha, 20, 'red') # call the square function alisha.penup() # pick up the pen alisha.goto(40,0) # move to (40, 0) alisha.pendown() # put down the pen square(alisha,40) # draw another square alisha.penup() # pick up the pen alisha.goto(-100,0) # move to (-100, 0) alisha.pendown() # put down the pen square(alisha,100, 'blue') # draw another square

You can change the size of the screen object, set a background color for the screen, and set the code to not exit until you click the window. You need to do this when you run turtle code outside of the ebook otherwise the program will run but exit before you can even see the result.

Run the code to see what it draws.

from turtle import * # use the turtle library def square(turtle, length = 100, color = 'green'): turtle.setheading(0) # set the heading to east turtle.fillcolor(color) turtle.begin_fill() for sides in range(4): # repeat the indented lines 4 times turtle.forward(length) # move forward by length turtle.right(90) # turn by 90 degrees turtle.end_fill() space = Screen(200,200) # create a larger turtle space space.bgcolor('yellow') # set the background color #space.exitonclick() # use outside of the ebook alisha = Turtle() # create a turtle named alisha square(alisha, 20, 'red') # call the square function alisha.penup() # pick up the pen alisha.goto(40,0) # move to (40, 0) alisha.pendown() # put down the pen square(alisha,40) # draw another square alisha.penup() # pick up the pen alisha.goto(-100,0) # move to (-100, 0) alisha.pendown() # put down the pen square(alisha,100, 'blue') # draw another square

Add a function to draw an equilateral triangle and then write a function to draw a simple house by calling the functions to draw a triangle and a square.

from turtle import * # use the turtle library def square(turtle, length = 100, color = 'green'): turtle.setheading(0) # set the heading to east turtle.fillcolor(color) turtle.begin_fill() for sides in range(4): # repeat the indented lines 4 times turtle.forward(length) # move forward by length turtle.right(90) # turn by 90 degrees turtle.end_fill() space = Screen() # create a turtle space t1 = Turtle() # create a turtle named t1

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