Variables

What is a variable?

A variable is a storage place that holds a value.

In other words, a variable lets you store a value, such as a number or string, in a place that you can refer back to using a name that you choose.

The value that is stored can vary -- hence the term variable.

Examples

For example, this line of code creates a variable named price and stores the number 39 in it:

price = 39

And this code creates a variable named username and stores the string "bob1964" in it:

username = "bob1964"

A variable is one of the basic concepts you'll need in nearly every program you write.

Try storing a number

This program defines and then prints a variable:

my_number = 123
print(my_number)

Try changing the program to instead store the number 999 in the variable before it is printed.

Create a variable from scratch

Write a line of code that stores the string "apple" into a variable named fruit.

Terminology

Here's the code again that defines the price variable:

price = 39

Here, price is the name of the variable, and 39 is the value of the variable.

Storing a value into a variable is called a variable assignment.

More complex variable assignments

The right-hand side of a variable assignment can be a number, a string, or another variable. It can even be an expression using + or *.

These are all valid variable assignments:

a = 100
b = a + a
c = b*3

x = "test"
y = x + x

Using multiple variables

Write a program consisting of four lines of code.

In the first line of code, store the number 20 in a variable named price.

In the second line of code, store the number 113 in a variable named amount.

In the third line of code, calculate price * amount and store it in a variable named total.

In the fourth line of code, print the value in the total variable.

Variable names

You can give a variable almost any name you want. For example, these lines are all valid Python code:

myVar = 123
x = 42
UPPERCASE = 1
empty_string = ""

However variable names cannot contain spaces.

Python programmers normally use all-lowercase names with underscores in place of spaces, such as in this example:

user_password = "secret"

Terminology practice

Let's practice using the terminology for variables.

Write a program with four lines of code.

The first line of code should be a variable assignment. The variable should have the name word1 and the value "moon".

The second line of code should be a variable assignment with the name word2 and the value "light".

The third line should use + to concatenate word1 and word2 and store the result into a variable named combination.

The fourth line should print the value stored in the combination variable.

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