Lesson 4: Variables and Data Types

Programming isn't just about printing text; it's about handling information. To do this, we use Variables. Think of a variable as a labeled box where you can store a piece of data so you can use it later.

Lesson Overview

In this lesson, we will:

• Create Variables: Learning how to "declare" and "assign" data.
• Explore Data Types: Understanding the difference between text, numbers, and logic.
• Variable Naming: The rules for naming your "boxes."
• Changing Variables: Seeing how data can evolve in a program.

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1. What is a Variable?

In Python, you create a variable by giving it a name and setting it equal to a value.

# Create a variable named 'username' and store the text "PixelCoder"
username = "PixelCoder"

# Create a variable named 'level' and store the number 10
level = 10

print(username)
print(level)

Key Concept: The = sign in Python doesn't mean "is equal to" (like in math). It means "Assign this value to this name."

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2. Basic Data Types

Python automatically figures out what kind of data you are storing. These are the four most common types:

A. Strings (str)

Used for text. Must always be inside quotes (single ' or double ").

name = "Alex"
message = 'Welcome to Python!'

B. Integers (int)

Used for whole numbers (positive or negative). No decimal points.

age = 25
score = -5

C. Floats (float)

Used for decimal numbers.

price = 19.99
pi = 3.14159

D. Booleans (bool)

Used for logic. Can only be True or False. (Note the capital letters!)

is_game_over = False
is_logged_in = True

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3. Why Data Types Matter

You can do different things with different types. For example, you can add two integers together, but you can't subtract a string from a boolean!

# Math with numbers
health = 100
damage = 20
remaining_health = health - damage # Result: 80

# Connecting strings (this is called concatenation)
greeting = "Hello " + "World" # Result: "Hello World"

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4. Variable Naming Rules

Python has a few rules for what you can name your variables:

1. Must start with a letter or an underscore _.
2. Cannot start with a number.
3. Can only contain letters, numbers, and underscores (no spaces or hyphens!).
4. Case-sensitive: Name and name are two different boxes.

Pro Tip (Snake Case): In Python, we usually use underscores to separate words in variable names, like player_score or is_user_authorized.

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Practice Exercise: The Personal Profile

Create a new file named profile.py. Create the following variables and print them:

1. first_name (a string)
2. last_name (a string)
3. age (an integer)
4. height_in_meters (a float)
5. loves_linux (a boolean)

Bonus: Try to add first_name and last_name together with a space in between to create a full_name variable!

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Quick Knowledge Check

1. What symbol do we use to assign a value to a variable?
2. What is the difference between an integer and a float?
3. Which of these names is invalid: user_1, 1_user, or _user?
4. What data type would you use to store whether a user has a subscription?

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Key Takeaways

• Variables store information for later use.
• The assignment operator is =.
• Strings = Text, Integers = Whole Numbers, Floats = Decimals, Booleans = True/False.
• Python is case-sensitive and uses snake_case for naming.

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What’s Next?

We know how to store data, but how do we get data from the user? In Lesson 5, we’ll learn about Input and Output to make our programs interactive!