4.mp4

Functions with parameters

In this section you’ll use the Python turtle drawing library to draw some circles, and then use functions and parameters to improve your code.

First you need to import the turtle library and create a Turtle object to draw with. I’ve called mine tina. You can use any name you like, and even have multiple turtle objects with different names.

from turtle import Turtle

tina = Turtle()

To draw a circle with the turtle, you can use the dot function, which takes a diameter (in pixels) as an input parameter.

tina.dot(100)

Usually you would describe a circle using the radius instead of the diameter, so now I’d like you to define a function that allows you to provide the radius. The function will also need the name of a turtle to draw with, allowing this function to be used on any turtle your program might have.

def draw_circle(t_name, r):

t_name.dot(r*2)

This function has a longer name, but it’s clear what it will do. When I call the function, it changes the state of the world by drawing a circle on the screen, with the given turtle.

from turtle import Turtle

tina = Turtle()

def draw_circle(t_name, r):

t_name.dot(r*2)

draw_circle(tina, 50)

I want to be able to draw colourful circles too, so I’ll add a parameter for the colour. The turtle recognises lots of strings as colour names, such as "red", "green", and "violet". Parameters can be strings, so you’ll need to add a parameter for the colour name and pass colour names as strings.

def draw_circle(t_name, r, col):

t_name.color(col)

t_name.dot(r*2)

The turtle library uses the US spelling of ‘colour’ for the color function, which sets the colour of the turtle.

Now you can create coloured circles.

draw_circle(tina, 150, "blue")

draw_circle(tina, 100, "red")

draw_circle(tina, 50, "yellow")

Challenges:

Try out one or more of these challenges:

At the moment all of your circles are drawn at the centre of the screen. Can you add parameters to the draw_circle function so that you can draw circles at different locations on the screen?

a. The goto(x, y) function moves the turtle to a specific location.
b. The penup() function lifts the pen so that the turtle doesn’t draw when it’s moving.
c. What do you think is the best order for the input parameters for your function?
Can you create a similar function that draws rectangles of different sizes and shapes? You can look at the Modern Art project for help with drawing rectangles.
Use your functions to draw a picture or create some art.

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