Python if Statement

The if statement is used to execute a block of code only when a specified condition is True. It is one of the basic decision-making statements in Python.

The if statement evaluates a condition. If the condition is true, the statements inside the if block are executed. If the condition is false, the block is skipped.

Syntax of if Statement

if condition:
    statement

The colon : after the condition indicates the beginning of the if block. Python uses indentation to identify the statements belonging to the block.

Simple if Statement

age = 20

if age >= 18:
    print("You are eligible to vote.")

You are eligible to vote.

Since age >= 18 is True, the print() statement is executed.

if Statement with a False Condition

age = 15

if age >= 18:
    print("You are eligible to vote.")

print("Program completed.")

Program completed.

The condition is false, so the statement inside the if block is not executed. The statement outside the block is executed.

if Statement with Comparison Operators

Comparison operators can be used to create conditions in an if statement.

marks = 75

if marks >= 40:
    print("Pass")

Pass

The condition marks >= 40 evaluates to True, so the message is displayed.

if Statement with Equality Operator

number = 10

if number == 10:
    print("Number is 10")

Number is 10

if Statement with Logical Operators

Logical operators such as and, or and not can be used to combine conditions.

Using and

age = 25

if age >= 18 and age <= 60:
    print("Eligible")

Eligible

Using or

day = "Sunday"

if day == "Saturday" or day == "Sunday":
    print("Weekend")

Weekend

Using not

is_raining = False

if not is_raining:
    print("You can go outside.")

You can go outside.

if Statement with User Input

The input() function can be used to accept a value from the user and then apply a condition.

age = int(input("Enter your age: "))

if age >= 18:
    print("You are an adult.")

Enter your age: 21
You are an adult.

Checking Positive Number

number = int(input("Enter a number: "))

if number > 0:
    print("Positive number")

Enter a number: 25
Positive number

Checking Even Number

The modulus operator % can be used to determine whether a number is even.

number = int(input("Enter a number: "))

if number % 2 == 0:
    print("Even number")

Enter a number: 20
Even number

Checking Whether a String is Empty

An empty string evaluates to False in a Boolean context.

name = input("Enter your name: ")

if name:
    print("Name entered:", name)

Enter your name: Rahul
Name entered: Rahul

if Statement with Membership Operator

The in operator can be used to check whether an item exists in a sequence.

fruits = ["apple", "banana", "mango"]

if "mango" in fruits:
    print("Mango is available.")

Mango is available.

Nested if Statement

An if statement inside another if statement is called a nested if statement.

age = 25
has_id = True

if age >= 18:
    if has_id:
        print("Entry allowed.")

Entry allowed.

The inner if statement is checked only when the outer condition is true.

Multiple Statements inside if Block

More than one statement can be placed inside an if block. All statements must have the same indentation.

marks = 85

if marks >= 40:
    print("Result: Pass")
    print("Congratulations!")
    print("You have cleared the examination.")

Result: Pass
Congratulations!
You have cleared the examination.

Importance of Indentation

Python uses indentation to define a block of code. Statements belonging to the if block must be indented.

age = 20

if age >= 18:
    print("Adult")
    print("Eligible")

In this example, both print() statements belong to the if block because they have the same indentation.

if Statement with Multiple Conditions

marks = 85

if marks >= 40 and marks <= 100:
    print("Valid passing marks")

Valid passing marks

Checking a Number in a Range

Python allows comparison expressions to be chained.

number = 50

if 1 <= number <= 100:
    print("Number is between 1 and 100.")

Number is between 1 and 100.

Practical Example: Discount Eligibility

amount = float(input("Enter purchase amount: "))

if amount >= 5000:
    print("You are eligible for a discount.")

Enter purchase amount: 6500
You are eligible for a discount.

Practical Example: Pass Check

marks = int(input("Enter marks: "))

if marks >= 40:
    print("Pass")

Enter marks: 72
Pass

if Statement vs if-else Statement

The if-else statement is discussed in the next tutorial.

Important Points

• The if statement is used for decision making.
• The condition is evaluated as either True or False.
• The colon : is required after the condition.
• Statements inside the if block must be indented.
• Comparison operators can be used to create conditions.
• Logical operators can combine multiple conditions.
• An if statement can be nested inside another if statement.
• The if statement does not provide an alternative block when the condition is false.