7.4. Practice Makes Perfect

Here’s a reminder of the drawing commands we’ve learned so far:

Drawing commands	What does it do?
forward( distance )	Move forward a specified distance
backward( distance )	Move backward a specified distance
left(90)	Turns 90 degrees to the left (you can use any angle, not just 90!)
right(90)	Turns 90 degrees to the right
circle( radius )	Draws a circle with the specified radius
goto( x, y )	Move straight to the position with coordinates (x, y). Note: the center is (0, 0)
up()	Stop leaving a trail
down()	Start drawing a trail
color( c )	Set the color to c (https://trinket.io/docs/colors)
begin_fill()	Starts filling in drawn shapes
end_fill()	Stops filling in drawn shapes
speed(number 0-10)	Determines how quickly the turtle will move through commands

Functions and Loops

Drawing commands	What does it do?
for i in range( n ):	Repeat n times
def function_name():	Creates and defines a new function
function_name()	Calls a function

Variables

Command	What does it do?
variable = value	Stores the value in your variable
variable = input( message )	Takes user input and stores it in your variable

7.4.1. Quick review of variables:

• A variable is a container that stores a value

• You can access that value by calling your variable by its name

• You can change the value that’s stored in a variable with the equal sign “=”

Take a look at the example below that draws 3 circles in a row that are the same size without a variable versus with a variable.

import turtle # move the turtle to the starting position turtle.speed(10) turtle.up() turtle.backward(150) turtle.down() # draw three circles WITHOUT a variable turtle.circle(50) turtle.forward(100) turtle.circle(50) turtle.forward(100) turtle.circle(50) # move to next starting position turtle.up() turtle.goto(-150, -150) turtle.down() # use a variable to define the radius of your next three circles rad = 30 turtle.circle(rad) turtle.forward(100) turtle.circle(rad) turtle.forward(100) turtle.circle(rad) # try adding a second variable to that last block of code for the distance forward

Building off of this idea, can we draw a square that uses a variable for the length of its sides?

import turtle side_length = 50 # draw your square using the side_length variable here

7.4.2. Parameters

Parameters allow us to use variables to make functions more customizable. When we call turtle.circle(50) we give it a value for the radius of the circle. We can do this when we define our own functions too.

Let’s try it out by writing a function that draws a square with a side length of our choice. Use your code from the previous exercise as a starting point.

import turtle def square(): # draw your square here

Once you’ve got the above code working, try adding a second parameter that sets the color of the square!

How else can we use parameters? Let’s define a shape() function that has a parameter for the number of sides for the shape. (So shape(3) draws a triangle, shape(4) draws a square, etc)

import turtle def shape(sides): # draw the shape here # this draws a triangle shape(3) # this draws a square shape(4)

7.4.3. Have Some Fun!

With what time we have left, take what you’ve learned and have some fun experimenting with drawing something cool! If you need some inspiration, check out the examples below! And, as always, ask a mentor if you get stuck or need any tips!

import turtle # have fun! :)

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