Variables for Your Drawing

By the end of this lesson you'll be able to:

• Store a number in a variable and use it in your code
• Change the size of a square by editing just one line
• Explain why variables make programs easier to modify

In the simple square lesson, the numbers 100 and 90 appeared eight times each. If you wanted a bigger square you had to change eight lines. Variables let you write the number once and use it everywhere — change the variable and the whole drawing changes.

Welcome to This Lesson!

Ready to make your code smarter? Today I'll show you how variables work — and why every programmer uses them. Let's code it together!

What Is a Variable?

A variable is a named box that holds a value. You create one by writing a name, an equals sign, and the value:

distance = 100

After this line, Python remembers that distance equals 100. Whenever you write distance later in your code, Python uses 100 in its place.

Give variables descriptive names — distance is much clearer than d or x.

Scratch Bridge

In Scratch you used the "Set [distance] to 100" block in the Variables drawer. In Python, distance = 100 does exactly the same thing: it creates a variable called distance and stores the value 100 in it.

Sample Code

import turtle
monty = turtle.Turtle()
monty.shape('turtle')

distance = 100
angle = 90

monty.forward(distance)
monty.right(angle)

monty.forward(distance)
monty.right(angle)

monty.forward(distance)
monty.right(angle)

monty.forward(distance)
monty.right(angle)

What Do You Think Will Happen?

The turtle uses distance for every forward() call and angle for every right() call. What shape will it draw? Make your guess — then click Run to find out!

Try It Now

Edit the code below and click Run to see Monty draw right on this page. No account needed — everything runs in your browser.

▶ Run ↻ Reset

Were you right? With angle = 90, each turn is a quarter-circle, so the turtle draws a perfect square.

If you see a red error message: Check that your variable name is spelled exactly the same everywhere — distance and Distance are two different names in Python.

How It Works

Python reads the file from top to bottom. When it reaches distance = 100, it stores the value 100 in memory under the name distance. Every time it later sees forward(distance), it looks up that stored value and uses it — just like reading a note you left yourself.

Explanation Table

Line	What it does
distance = 100	Creates a variable named distance and stores 100 in it
angle = 90	Creates a variable named angle and stores 90 in it
monty.forward(distance)	Moves forward 100 steps (reads the variable's value)
monty.right(angle)	Turns 90 degrees right (reads the variable's value)

Common Mistake: Typo in Variable Name

If you write distanse on one line and distance on another, Python treats them as two different variables — and the second one has no value yet. You'll see a NameError. Python is case-sensitive too: Distance ≠ distance.

Learning Check

Spot the Bug!

The program below should draw a square, but it crashes with a NameError. There's a typo in one variable name. Can you find it and fix it?

▶ Run ↻ Reset

Experiments

Try these changes to the code above. Predict what will happen first, then run it to check!

1. Change distance = 100 to distance = 150. You'll know it worked when the square is noticeably larger than before.

2. Change distance = 100 to distance = 40. You'll know it worked when the square is about half as big.

3. Change angle = 90 to angle = 120 and reduce the four pairs to three pairs of forward/right. You'll know it worked when you see a triangle instead of a square.

4. Add monty.color('purple') just before the first forward line. You'll know it worked when all four sides of the square are purple.

5. Add a third variable: monty.pensize(thickness) and set thickness = 5 at the top. You'll know it worked when the lines are noticeably thicker, and you can change thickness in one place to affect all four sides.

Great Work!

You've unlocked variables — one of the most powerful ideas in all of programming! In the next lab you'll combine variables with a for loop so you don't have to repeat those four lines at all. Let's code it together!