Python Variables

📦 Understanding Variables

Variables are containers for storing data values. In Python, variables are created when you assign a value to them. They're like labeled boxes where you can store different types of information and retrieve them later.


# Creating a variable
name = "John"
print(name)  # Output: John

Dynamic

Typing

Flexible

Storage

Easy

Assignment

Creating Variables

Python has no command for declaring a variable. A variable is created the moment you first assign a value to it.

📝

String Variables

Store text data

name = "Alice"
message = 'Hello, World!'

🔢

Numeric Variables

Store numbers (int, float)

age = 25
height = 5.6

✅

Boolean Variables

Store True/False values

is_student = True
has_license = False

📊

Dynamic Typing

Type changes automatically

x = 10      # int
x = "text"  # now string

Variable Types

Python variables can store different types of data. The type is determined automatically based on the value assigned.

🔤

String (str)

Text data enclosed in quotes

message = "Hello, World!"
single_quotes = 'Python is awesome'
multiline = """This is a
multiline string"""

🔢

Integer (int)

Whole numbers without decimals

count = 42
negative = -17
zero = 0

🎯

Float (float)

Numbers with decimal points

price = 19.99
pi = 3.14159
scientific = 2.5e4  # 25000.0

✅

Boolean (bool)

True or False values

is_active = True
is_complete = False
result = 5 > 3  # True

Checking Variable Types

You can check the type of any variable using the type() function.

Using type() Function

# Create variables of different types
name = "Python"
version = 3.11
is_popular = True
users = 1000000

# Check their types
print(f"name is of type: {type(name)}")           # 
print(f"version is of type: {type(version)}")     # 
print(f"is_popular is of type: {type(is_popular)}")# 
print(f"users is of type: {type(users)}")         # 

# You can also use isinstance() to check if a variable is of a specific type
print(f"Is name a string? {isinstance(name, str)}")        # True
print(f"Is version an integer? {isinstance(version, int)}")# False
print(f"Is users a number? {isinstance(users, (int, float))}")# True

Variable Naming Rules

Python has specific rules for naming variables and follows conventions that make code more readable.

✅ Valid Variable Names

name = "Alice"
age = 25
user_name = "alice123"
first_name = "Alice"  # snake_case (preferred)
PI = 3.14159  # constants in UPPERCASE

❌ Invalid Variable Names

# These will cause SyntaxError
2name = "Alice"      # starts with number
first-name = "Alice" # contains hyphen
class = "Python"     # reserved keyword

Variable Naming Rules

Python has specific rules for naming variables that you must follow:

✅

Valid Names

# Valid variable names
name = "Alice"
age = 25
first_name = "John"
lastName = "Doe"  # camelCase
_private = "hidden"
PI = 3.14159
user123 = "user"
my_var_2 = "value"

❌

Invalid Names

# Invalid variable names (will cause errors)
# 2name = "Alice"      # Can't start with number
# first-name = "John"  # Can't contain hyphens
# class = "Python"     # Can't use reserved keywords
# my name = "Alice"    # Can't contain spaces
# @variable = "value"  # Can't contain special characters

🎯 Naming Best Practices

Use descriptive names:

x = 25 student_age = 25

Use snake_case for variables:

firstName first_name

Use UPPER_CASE for constants:

max_size = 100 MAX_SIZE = 100

Avoid single letters (except for loops):

n = "John" name = "John"

Multiple Assignment

Python allows you to assign values to multiple variables in different ways:

Multiple Assignment Techniques

🔹 Assign Same Value to Multiple Variables

x = y = z = 10
print(f"x={x}, y={y}, z={z}")  # x=10, y=10, z=10

🔹 Assign Different Values to Multiple Variables

a, b, c = 1, 2, 3
print(f"a={a}, b={b}, c={c}")  # a=1, b=2, c=3

🔹 Unpacking a List or Tuple

coordinates = (10, 20)
x_pos, y_pos = coordinates
print(f"Position: ({x_pos}, {y_pos})")  # Position: (10, 20)

🔹 Swapping Variables

first = "Hello"
second = "World"
print(f"Before swap: first='{first}', second='{second}'")

first, second = second, first  # Swap values
print(f"After swap: first='{first}', second='{second}'")

🔹 Unpacking with Asterisk

numbers = [1, 2, 3, 4, 5]
first, *middle, last = numbers
print(f"First: {first}")    # First: 1
print(f"Middle: {middle}")  # Middle: [2, 3, 4]
print(f"Last: {last}")      # Last: 5

Global vs Local Variables

Variables can have different scopes - they can be global (accessible everywhere) or local (accessible only within a function).

Basic Variable Scope

# Example 1: Basic Global vs Local
message = "Hello World!"  # Global variable

def greet():
    name = "Alice"  # Local variable
    print(message)  # Can access global
    print(name)     # Can access local

greet()

Modifying Global Variables

# Example 2: Using global keyword
score = 0

def update_score():
    global score
    score += 10
    print(f"Score: {score}")

update_score()  # Score: 10
print(f"Final score: {score}")  # Final score: 10

Variable Operations

You can perform various operations with variables depending on their types:

🔢

Numeric Operations

a = 10
b = 3

print(f"Addition: {a + b}")      # 13
print(f"Subtraction: {a - b}")   # 7
print(f"Multiplication: {a * b}")# 30
print(f"Division: {a / b}")      # 3.33...
print(f"Floor Division: {a // b}")# 3
print(f"Modulus: {a % b}")       # 1
print(f"Exponentiation: {a ** b}")# 1000

🔤

String Operations

first_name = "John"
last_name = "Doe"

# String concatenation
full_name = first_name + " " + last_name
print(full_name)  # John Doe

# String repetition
greeting = "Hello! " * 3
print(greeting)   # Hello! Hello! Hello! 

# String formatting
age = 25
message = f"My name is {full_name} and I'm {age} years old"
print(message)

✅

Boolean Operations

is_sunny = True
is_warm = False

# Logical operations
print(f"Sunny AND Warm: {is_sunny and is_warm}")  # False
print(f"Sunny OR Warm: {is_sunny or is_warm}")    # True
print(f"NOT Sunny: {not is_sunny}")               # False

# Comparison operations
x = 5
y = 10
print(f"x > y: {x > y}")    # False
print(f"x < y: {x < y}")    # True
print(f"x == y: {x == y}")  # False

📋

List Operations

fruits = ["apple", "banana"]
vegetables = ["carrot", "broccoli"]

# List concatenation
food = fruits + vegetables
print(food)  # ['apple', 'banana', 'carrot', 'broccoli']

# List repetition
repeated = ["hello"] * 3
print(repeated)  # ['hello', 'hello', 'hello']

# List modification
fruits.append("orange")
print(fruits)  # ['apple', 'banana', 'orange']

🏋️ Practice Exercise: Personal Budget Calculator

Let's create a practical example that demonstrates various variable concepts:

Student Information System

# Simple Variable Examples
# Shows basic variable usage in Python

# String variables
name = "John"
greeting = "Hello"

# Number variables 
age = 25
height = 1.75

# Boolean variable
is_student = True

# Basic calculations
birth_year = 2024 - age
next_year_age = age + 1

# Using variables together
message = f"{greeting}, {name}!"
height_in_feet = height * 3.28

# Display information
print("=" * 30)
print("Personal Information")
print("=" * 30)
print(f"Name: {name}")
print(f"Age: {age}")
print(f"Height: {height_in_feet:.1f} feet")
print(f"Birth Year: {birth_year}")
print(f"Next year's age: {next_year_age}")
print(f"Student: {'Yes' if is_student else 'No'}")
print(f"Message: {message}")

# Show variable types
print("\nVariable Types:")
print(f"name is type: {type(name)}")
print(f"age is type: {type(age)}")
print(f"height is type: {type(height)}")
print(f"is_student is type: {type(is_student)}")

Real-World Example: Student Information System

Let's create a practical example that demonstrates various variable concepts:

📦 Understanding Variables

Creating Variables

String Variables

Numeric Variables

Boolean Variables

Dynamic Typing

Variable Types

String (str)

Integer (int)

Float (float)

Boolean (bool)

Checking Variable Types

Variable Naming Rules

✅ Valid Variable Names

❌ Invalid Variable Names

Variable Naming Rules

Valid Names

Invalid Names

🎯 Naming Best Practices

Multiple Assignment

🔹 Assign Same Value to Multiple Variables

🔹 Assign Different Values to Multiple Variables

🔹 Unpacking a List or Tuple

🔹 Swapping Variables

🔹 Unpacking with Asterisk

Global vs Local Variables

Variable Operations

Numeric Operations

String Operations

Boolean Operations

List Operations

🏋️ Practice Exercise: Personal Budget Calculator

Real-World Example: Student Information System

🧠 Test Your Knowledge

Which of the following is a valid Python variable name?

What function is used to check the type of a variable in Python?

What happens when you assign the same value to multiple variables like `x = y = z = 5` ?

📦 Understanding Variables

Creating Variables

String Variables

Numeric Variables

Boolean Variables

Dynamic Typing

Variable Types

String (str)

Integer (int)

Float (float)

Boolean (bool)

Checking Variable Types

Variable Naming Rules

✅ Valid Variable Names

❌ Invalid Variable Names

Variable Naming Rules

Valid Names

Invalid Names

🎯 Naming Best Practices

Multiple Assignment

🔹 Assign Same Value to Multiple Variables

🔹 Assign Different Values to Multiple Variables

🔹 Unpacking a List or Tuple

🔹 Swapping Variables

🔹 Unpacking with Asterisk

Global vs Local Variables

Variable Operations

Numeric Operations

String Operations

Boolean Operations

List Operations

🏋️ Practice Exercise: Personal Budget Calculator

Real-World Example: Student Information System

🧠 Test Your Knowledge

Which of the following is a valid Python variable name?

What function is used to check the type of a variable in Python?

What happens when you assign the same value to multiple variables like x = y = z = 5 ?

What happens when you assign the same value to multiple variables like `x = y = z = 5` ?