1   What Is a Variable?

Imagine you are doing a maths problem on paper. You write "let x = 5" at the top. Now, every time you see x in the problem, you know what it means. A variable in Python works exactly the same way: you give a name to a value so you can refer to it later.

In Python, you create a variable by writing its name, an equals sign, and the value you want to store. This is called an assignment statement.

score = 10
player_name = "Alex"
temperature = 36.6

After these three lines run, Python remembers three things: a number called score, a piece of text called player_name, and a decimal number called temperature. You can now use those names anywhere in your program.

2   The Vocabulary of Variables

Before going further, let's nail down the key terms you will use — and hear — constantly when talking about variables.

3   Data Types

Not all values are the same kind of thing. The number 42 is different from the text "42". Python needs to know what kind of value is stored in a variable so it knows what operations make sense. This is called the variable's data type.

Here are the four core data types you will use constantly in Grade 9:

3.1   Integers (int)

Integers are whole numbers — no decimal point. They can be positive, negative, or zero. Use them for things you count: a score, a number of players, someone's age.

lives = 3
score = 0
year = 2026
temperature_celsius = -5

3.2   Floats (float)

Floats are numbers with a decimal point. Use them for things you measure: a height, a price, an average. Python automatically decides a number is a float the moment it sees a decimal point.

height_m = 1.75
price = 9.99
average_score = 84.5

3.3   Strings (str)

A string is any sequence of characters — letters, numbers, spaces, symbols — wrapped in quote marks. Both single quotes (') and double quotes (") work in Python.

first_name = "Alex"
city = 'Warsaw'
greeting = "Hello, world!"
zip_code = "00-001"   # This is a string, not a number — you'd never do maths with it

3.4   Booleans (bool)

A boolean is the simplest data type of all: it can only ever be True or False. Booleans are the foundation of decision-making in code — every if statement ultimately checks whether something is True or False.

game_over = False
is_logged_in = True
has_won = False

Notice that True and False are capitalised in Python. true (lowercase) will cause an error — Python is case-sensitive.

4   Naming Your Variables

You have a lot of freedom in naming variables, but there are rules and conventions you must know. Breaking the rules causes errors. Ignoring the conventions makes your code hard for others (and future-you) to read.

4.1   The Rules (Python enforces these)

4.2   The Conventions (the Python community expects these)

Conventions are not enforced by Python — your code will run either way. But good programmers follow them because they make code easier to read for everyone.

5   Assignment and Re-assignment

When you first store a value in a variable, that is called assignment. When you store a new value into a variable that already has one, that is called re-assignment. The old value is gone — overwritten.

score = 0          # Assignment: score is created and set to 0
print(score)       # Output: 0

score = 10         # Re-assignment: the old value (0) is replaced by 10
print(score)       # Output: 10

score = score + 5  # Re-assignment using the old value to calculate the new one
print(score)       # Output: 15

That last line is worth pausing on: score = score + 5. In maths class, this would be nonsense. But in Python, the right side is always evaluated first. Python reads it as: "take the current value of score (10), add 5 to it (giving 15), then store 15 back into score."

5.1   Shorthand Assignment Operators

Because updating a variable using its own value is so common, Python gives you shorthand operators:

You will see += constantly — in loops, games, counters, and totals. Get comfortable with it early.

6   Checking and Converting Types

Python gives you two useful built-in tools for working with types: one to check what type a variable is, and a set of functions to convert between types.

6.1   Checking a Type with type()

The type() function tells you exactly what data type a variable holds. This is particularly useful when debugging.

age = 15
name = "Alex"
height = 1.75
is_enrolled = True

print(type(age))          # <class 'int'>
print(type(name))         # <class 'str'>
print(type(height))       # <class 'float'>
print(type(is_enrolled))  # <class 'bool'>

6.2   Converting Between Types

Sometimes you need to convert a value from one type to another. This is called type conversion (or casting). Python provides built-in functions for the most common conversions:

The most common place you will need type conversion is when working with user input. The input() function always returns a string, even if the user types a number. Forgetting this causes one of the most frequent beginner errors:

age = input("How old are you? ")   # User types 15 — but age is the STRING "15"
next_year = age + 1                 # ERROR: cannot add a string and an integer

# The fix: convert first
age = int(input("How old are you? "))
next_year = age + 1                 # Now this works: 15 + 1 = 16
print("Next year you will be", next_year)

7   Putting It Together: Variables in a Real Program

Here is a short but complete program that uses everything covered in this article. Read it carefully and try to predict the output before scrolling down.

player_name = input("Enter your name: ")
score = 0
lives = 3

print("Welcome,", player_name)
print("Score:", score, "| Lives:", lives)

score += 50
lives -= 1

print("--- After round 1 ---")
print("Score:", score, "| Lives:", lives)

final_message = player_name + " finished with a score of " + str(score)
print(final_message)

Notice a few things:

• score and lives are updated using += and -=.
• To combine player_name (a string) with score (an integer) in one line of text, we must convert score to a string first using str(score).
• Every variable has a clear, descriptive name — you can read the program almost like a sentence.

8   Final Check: The Big Picture

9   Quick-Reference Glossary