Variables are one of the most important concepts in Python. They are used to store data that can be used and modified throughout a program.

Think of a variable as a container that holds information. You can store values such as text, numbers, or other types of data inside a variable and use them whenever needed.

What is a Variable?

A variable is a name that refers to a value.

Example:

name = "John"
            

In this example:

• name is the variable name.
• "John" is the value stored in the variable.

You can display the value using the print() function:

name = "John" 
print(name)
            

Output:

John
            

Creating Variables

In Python, you do not need to declare the type of a variable before using it.

Simply assign a value using the equals sign (=):

age = 25 
city = "Delhi" 
price = 99.99
            

Python automatically determines the data type based on the assigned value.

Variable Types

Python variables can store different types of data.

String (Text)

name = "Alice"
            

Strings are used to store text.

Integer (Whole Numbers)

age = 20
            

Integers store whole numbers.

Float (Decimal Numbers)

price = 19.99
            

Floats store numbers with decimal points.

Boolean (True or False)

is_active = True
            

Booleans represent logical values.

Displaying Variables

Use the print() function to display variable values.

name = "Alice" 
print(name)
            

Output:

Alice
            

You can also print multiple variables:

name = "Alice" 
age = 20 
print(name, age)
            

Output:

Alice 20
            

Changing Variable Values

Variable values can be changed at any time.

name = "Alice" 
name = "Bob" 
print(name)
            

Output:

Bob
            

The old value is replaced with the new one.

Assigning Multiple Variables

You can assign values to multiple variables in a single line.

name, age, city = "Alice", 20, "Delhi"
print(name)
print(age)
print(city)
            

Output:

Alice
20
Delhi
            

Assigning One Value to Multiple Variables

Python allows multiple variables to share the same value.

x = y = z = 100
print(x)
print(y)
print(z)
            

Output:

100
100
100
            

Variable Naming Rules

When naming variables, follow these rules:

Valid Variable Names

name = "John" 
user_age = 25 
totalPrice = 100
            

Invalid Variable Names

2name = "John" 
user-name = "John" 
class = "Python"
            

These are invalid because:

• Variable names cannot start with a number.
• Hyphens (-) are not allowed.
• Python keywords cannot be used as variable names.

Variable Naming Best Practices

Use meaningful names that describe the stored data.

Good:

student_name = "John" 
total_price = 500
            

Bad:

a = "John" 
x = 500
            

Descriptive names make your code easier to read and maintain.

Getting the Variable Type

Use the type() function to check the data type of a variable.

name = "John" 
print(type(name))
            

Output:

<class 'str'>
            

Examples:

age = 25 
print(type(age))
            

Output:

<class 'int'>
            

price = 19.99 
print(type(price))
            

Output:

<class 'float'>
            

Case-Sensitive Variables

Python treats uppercase and lowercase letters differently.

name = "John" 
Name = "Alice" 
print(name) 
print(Name)
            

Output:

John Alice
            

Here, name and Name are two different variables.

Global Variables

A variable created outside of a function is called a global variable. Global variables can be accessed from anywhere in the program, including inside functions.

Example

name = "John" 
def greet(): 
    print("Hello,", name) 

greet()
            

Output:

Hello, John
            

In this example, the variable name is defined outside the function, so it can be used inside the greet() function.

Creating a Global Variable Inside a Function

Normally, variables created inside a function are local and can only be used within that function. To create a global variable inside a function, use the global keyword.

def create_user(): 
    global username 
    username = "Alice"
create_user() 
print(username)
            

Output:

Alice
            

Modifying a Global Variable

To change the value of a global variable inside a function, you must use the global keyword.

count = 10 
def update_count(): 
    global count 
    count = 20 
update_count() 
print(count)
            

Output:

20
            

Constants in Python

Python does not have true constants, but developers usually use uppercase variable names to indicate that a value should not change.

PI = 3.14159 
MAX_USERS = 100
            

This is a naming convention and not enforced by Python.

Real-World Example

student_name = "Rahul"
age = 18
course = "Python"

print("Student:", student_name)
print("Age:", age)
print("Course:", course)

Output:
            

Output:

Student: Rahul
Age: 18
Course: Python
            

Summary

• Variables are used to store data.
• Create variables using the equals sign (=).
• Python automatically determines the data type.
• Variable values can be changed at any time.
• Use meaningful variable names.
• Variable names are case-sensitive.
• Use type() to check a variable's data type.

Variables are the foundation of Python programming, and understanding them is essential before moving on to data types, operators, and control structures.