Variables

Variables are used to store data and the contents of them can be changed. This could be strings (text), numbers (integers, floats / decimals), or booleans (true or false).

Variables must start with a letter.

When naming variables (and functions) in Python we use an _ to separate different words.

For example a variable to store a person's first name could be first_name

We cannot start variables with a number.

In programming the = symbol is known as the assignment operator. It is used to assign (store) data in a variable.

We assign what is on the right of the = to the variable on the left of the =.

To the right of the = we can carry out the processing to modify the data to store in the variable.

Below are five examples of variables that have data stored in them.

first_name = "Lenny"
surname = "Learner"
age = 15
account_balance = 3.50
is_gamer = True

We can change the data stored in a variable as shown below.

Lines 2 and 4 are to show the output that has changed.

price = 3.5
print("Price before: ", price)
price = 4
print("Price after: ", price)

Another thing that you might want to do with variables is switch the values between two variables.

For example if a = 5 and b = 10 we might want to switch them to a = 10 and b = 5

To achieve this we need to create a placeholder variable. If we don't do this and use the code below we will lose the contents of one vairable.

a = 5
b = 10
print("A: ", a, "B: ", b)
a = b
b = a
print("A: ", a, "B: ", b)

The code above will print

A: 5 B: 10
A: 10 B: 10

This isn't what we want.

The code below uses a placeholder value to temporarily hold the value of the variable that we are overwriting first.

a = 5
b = 10
print("A: ", a, "B: ", b)

temp = a
a = b
b = temp
print("A: ", a, "B: ", b)

Variables are really important and useful and will be used thoroughly throughout your programming journey.