Variables and Data Types

Friendly introduction

Imagine your computer is a backpack. Variables are like labeled pockets where you store different kinds of things. Some pockets hold whole numbers, some hold decimals, some hold words, and some hold true/false answers. In Python, these "kinds of things" are called data types.

In this lesson, you'll learn:

What variables are
The 4 basic data types: int, float, str, bool
How to use them in simple programs

What is a variable?

A variable is a name that stores a value in your program.

Example:

score = 10
player_name = "Alex"
is_game_over = False

print(score)
print(player_name)
print(is_game_over)

Tips for naming variables:

Use letters, numbers, and underscores (_) only.
Don't start with a number. Example: age2 is OK, 2age is not.
No spaces. Use underscores: total_apples
Python is case-sensitive: Age and age are different.

The 4 basic data types

a) int (integer)

Whole numbers (no decimals), like -5, 0, 12.

apples = 5
bananas = 3
total_fruit = apples + bananas
print(total_fruit)  # 8

b) float

Numbers with decimals, like 3.14, 2.0, -0.5.

price = 2.5
quantity = 3
cost = price * quantity
print(cost)  # 7.5

c) str (string)

Text inside quotes. You can use single ' or double " quotes.

greeting = "Hello"
name = 'Maya'
message = greeting + ", " + name + "!"
print(message)  # Hello, Maya!

d) bool (boolean)

True or False (must be capitalized).

is_raining = True
have_umbrella = False
need_umbrella = is_raining and not have_umbrella
print(need_umbrella)  # True

How to check a variable's type

Use the type() function to see what kind of data is stored.

age = 14
height = 1.62
nickname = "Sky"
is_student = True

print(type(age))       # <class 'int'>
print(type(height))    # <class 'float'>
print(type(nickname))  # <class 'str'>
print(type(is_student))# <class 'bool'>

Converting between types (casting)

Sometimes you need to change a value's type:

int(x): to an integer
float(x): to a float
str(x): to a string
bool(x): to a boolean

Examples:

# str to int
age_text = "14"
age_number = int(age_text)
print(age_number + 1)  # 15

# int to str for printing
points = 20
print("You have " + str(points) + " points.")  # You have 20 points.

# float to int (decimals get cut off)
pi = 3.14
print(int(pi))  # 3

# bool conversion
print(bool(0))      # False
print(bool(1))      # True
print(bool(""))     # False (empty string)
print(bool("Hi"))   # True (non-empty string)

Mini activity: Build a "Student Card"

Task:

Create these variables with your own info:
- name (str)
- age (int)
- height_m (float) e.g., 1.55
- has_bus_pass (bool) True or False
Print a neat summary in 2 lines:
- Line 1: Name and age next year
- Line 2: Height and whether you have a bus pass
Print the type of each variable using type().

Starter code:

# 1) Make variables
name = "YourNameHere"
age = 14
height_m = 1.60
has_bus_pass = True

# 2) Print a summary (try f-strings or +)
print("Name: " + name + " | Age next year: " + str(age + 1))
print("Height: " + str(height_m) + " m | Bus pass: " + str(has_bus_pass))

# 3) Check types
print(type(name))
print(type(age))
print(type(height_m))
print(type(has_bus_pass))

Optional challenge:

Change height_m to a string with 2 decimals. Hint: use round(height_m, 2) or format with f"{height_m:.2f}".

Summary

Variables store values you can use later.
int: whole numbers
float: decimals
str: text
bool: True/False
Use type() to check a variable's type.
Convert types with int(), float(), str(), bool() when needed.

Great job! You now know the building blocks for almost every Python program.

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