Python Variables & Data Types | Beginner Python Tutorial

Why Variables Are Essential

Variables are named containers that store data values in memory. Think of them as labeled boxes where you can store information your program needs.

Real World Analogy	Python Variable
Label on a storage box	`name = "Azeem"`
Number on a price tag	`age = 25`
Shopping list items	`fruits = ["apple", "banana"]`

name = "Azeem"          # String (text)
age = 25               # Integer (whole number)  
height = 5.9           # Float (decimal number)
is_student = True      # Boolean (True/False)
grades = [85, 92, 78]  # List (collection)
                

The 6 Core Data Types

Type	Example	Use Case	Mutable?
str	`"Hello World"`	Text, names, messages	No
int	`42`	Counts, IDs, ages	No
float	`3.14`	Prices, measurements	No
bool	`True`	Conditions, flags	No
list	`[1, 2, 3]`	Ordered collections	Yes
dict	`{"name": "Bob"}`	Key-value storage	Yes

Strings - Text Mastery

Basic String Operations

# Single & Double Quotes (interchangeable)
name = "Azeem"
greeting = 'Hello'

# Concatenation (+)
full_greeting = greeting + ", " + name  # "Hello, Azeem"

# Length
message_length = len("Python")  # 6

# Multi-line strings
poem = """Roses are red,
Violets are blue"""

print(poem)
                

f-Strings (Python 3.6+)

# OLD WAY (messy)
name = "Azeem"
age = 25
print("My name is " + name + " and I'm " + str(age) + " years old")

# NEW WAY (f-strings - CLEAN!)
print(f"My name is {name} and I'm {age} years old")
print(f"Next year: {age + 1}")  # Math works too!
                

Lists & Dictionaries

Lists - Ordered Collections

# Create lists
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]

# Access by index (starts at 0)
print(fruits[0])    # "apple"
print(fruits[-1])   # "cherry" (last item)

# Modify lists (MUTABLE)
fruits[1] = "blueberry"
fruits.append("orange")

# Slicing
print(fruits[1:3])  # ["blueberry", "cherry"]
                

Dictionaries - Key-Value Power

# Create dictionary
student = {
    "name": "Azeem",
    "age": 25,
    "grades": [85, 92, 88],
    "active": True
}

# Access values
print(student["name"])      # "Azeem"
print(student.get("age"))   # 25 (safer)

# Add/Update
student["city"] = "NYC"
student["age"] = 26

# Check existence
if "email" in student:
    print("Has email")
                

Tuples - Immutable Lists

Tuples are like lists but cannot be modified. Perfect for fixed data like coordinates or configuration values.

# Coordinates (immutable)
location = (40.7128, -74.0060)  # NYC
lat, lon = location              # Unpacking

print(f"Lat: {lat}, Lon: {lon}")

# Multiple assignment
name, age, city = "Bob", 30, "LA"
print(f"{name} is {age} from {city}")
                

Practice Exercises

Exercise 1: Personal Profile

Create variables for your name, age, favorite color, and skills list. Print a formatted introduction using f-strings.

# YOUR CODE HERE
name = "YOUR_NAME"
# ... complete the exercise
                    

Exercise 2: Shopping Cart

Build a shopping cart dictionary with items and prices. Calculate total cost and add tax.

Exercise 3: Student Gradebook

Create a gradebook dictionary with multiple students. Calculate class average and find top performer.

Common Mistakes

# ❌ WRONG - Don't do this
age = 25
age = age + 1  # Creates new variable
                    

# ✅ CORRECT - Use +=
age = 25
age += 1  # age = age + 1 (cleaner)
                    

Type Conversion

# Convert between types
age_str = "25"          # String
age_int = int(age_str)  # Convert to int: 25

price = 19.99
price_int = int(price)  # Truncates: 19

is_active = bool(1)     # True
is_empty = bool("")     # False
                

You've Mastered Variables!

✅ What You Can Now Build:

Personal Info App
Store & display user data

Shopping Cart
Items, prices, totals

Student Gradebook
Multiple students & averages

Configuration Manager
Settings & preferences

Next Steps: Control Flow (if/else, loops) → Functions → Real Projects

Variables & Data Types

Master Variables & Data Types