Lesson 3: Variables & Data Types
Learn how to store and work with different types of information in Python
Beginner | 15 minWhat are Variables?
A variable is like a labeled box where you can store information. You can put data in it, change it, and use it later!
Think of it like:
- A box with a label (variable name)
- Contents inside the box (the value)
- You can change what's inside anytime
Creating Your First Variable
# Creating variables is super easy!
name = "Alice"
age = 25
height = 5.6
is_student = True
name = "Alice"
age = 25
height = 5.6
is_student = True
Variable Naming Rules:
- Start with a letter or underscore (not a number)
- Can contain letters, numbers, underscores
- Case-sensitive (name ≠ Name)
- No spaces (use underscores: my_variable)
- Avoid Python keywords (if, for, while, etc.)
Python Data Types
1. Integer (int)
Whole numbers without decimals
age = 25
year = 2025
score = -10
year = 2025
score = -10
2. Float (float)
Numbers with decimal points
height = 5.9
price = 19.99
temperature = -3.5
price = 19.99
temperature = -3.5
3. String (str)
Text data in quotes
name = "John"
city = 'New York'
message = "Hello World!"
city = 'New York'
message = "Hello World!"
4. Boolean (bool)
True or False values
is_active = True
has_permission = False
has_permission = False
Using Variables
# Create variables
name = "Sarah"
age = 22
# Use them
print("My name is", name)
print("I am", age, "years old")
name = "Sarah"
age = 22
# Use them
print("My name is", name)
print("I am", age, "years old")
Output:
My name is Sarah
I am 22 years old
My name is Sarah
I am 22 years old
Changing Variable Values
score = 10
print(score) # 10
score = 20
print(score) # 20
score = score + 5
print(score) # 25
print(score) # 10
score = 20
print(score) # 20
score = score + 5
print(score) # 25
Checking Data Types
print(type(25)) #
print(type(3.14)) #
print(type("Hello")) #
print(type(True)) #
print(type(3.14)) #
print(type("Hello")) #
print(type(True)) #
Interactive Quiz!
Q1: Which is a valid variable name?
A) 2name
B) my_name
C) my-name
D) my name
Q2: What data type is 3.14?
A) Integer
B) Float
C) String
D) Boolean
Q3: What does this print? x = 5; x = x + 3; print(x)
A) 5
B) 3
C) 8
D) 53
Practice Challenge
Your Task: Create variables for:
- Your name (string)
- Your age (integer)
- Your height in feet (float)
- Whether you like Python (boolean)
Then print them all!
Key Takeaways
- Variables store data
- Python has 4 main types: int, float, str, bool
- Use = to assign values
- Variables can be changed anytime
- Use type() to check data types
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