Variables

Introduction

Whew. Experimenting with the angles requires you to change three different places each time. Imagine you’d want to experiment with the square sizes, let alone with rectangles! We can do better than that.

This is where variables come into play: You can tell Python that from now on, whenever you refer to a variable, you actually mean something else. That concept might be familiar from symbolic maths, where you would write: Let x be 5. Then x * 2 will obviously be 10.

In Python syntax, that very statement translates to:

x = 5

After that statement, if you do print(x), it will actually output its value — 5. You can well use that for turtle too:

turtle.forward(x)

Note

You can not only save numbers in variables, like we did here for x, but you can actually save various kinds of things in them. A typical other thing you want to have stored often is a string - a line of text. Strings are indicated with a starting and a leading \" (double quote). You’ll learn about this and other types, as those are called in Python, and what you can do with them later on.

A variable called angle

Exercise

If we have a variable called angle, how could we use that to experiment much faster with our tilted squares program?

Solution

angle = 20

turtle.left(angle)

turtle.forward(50)
turtle.left(90)
turtle.forward(50)
turtle.left(90)
turtle.forward(50)
turtle.left(90)
turtle.forward(50)
turtle.left(90)

turtle.left(angle)
# ...

Bonus

Can you apply that principle to the size of the squares, too?

The house of santa claus

Exercise

Draw a house.

You can calculate the length of the diagonal line with Pythagoras. That value is a good candidate for a variable. To calculate the square root of a number in Python, import the math module and use the math.sqrt() function. The square of a number is calculated with the ** operator:

import math

c = math.sqrt(a**2 + b**2)