If Statement

Introduction

A computer program normally executes statement by statement, from top to bottom, in a fixed sequence. However, real programs rarely follow a single straight path — they must react differently depending on circumstances. For example:

• Only give a discount if the purchase amount is above ₹1000.
• Only allow login if the password is correct.
• Only print a warning if the battery is below 20%.
• Only send an alert if the temperature exceeds 40°C.

The if statement is Python's most basic decision-making tool. It allows a program to execute a block of statements only if a given condition evaluates to True. If the condition is False, the block is simply skipped, and the program continues with whatever comes next.

Syntax of If Statement

The syntax of a simple if statement is:

if condition:
    # statements to execute if condition is True
    statement_1
    statement_2

The statement begins with the keyword if, followed by a conditional expression that evaluates to True or False, and ends with a colon (:). All statements inside the conditional block must be indented at the same level.

Indentation in Python

Unlike many programming languages (like C, C++, or Java) that use curly braces {} to group statements, Python uses indentation (spaces or tabs) to define which statements belong to a block. All statements within the same block must share the same level of indentation — the standard convention is 4 spaces.

Correct vs Incorrect Indentation

if x > 0:
    print("Positive")
    print("Value accepted")

if x > 0:
    print("Positive")
      print("Value accepted")

Logic Flow

When the program encounters an if statement, Python performs the following steps:

1. It evaluates the condition expression.
2. If the condition is True, the indented block is executed.
3. If the condition is False, the block is skipped, and execution continues with the first unindented statement following the block.

Code Examples

1. Voting Eligibility

age = 20
if age >= 18:
    print("You are eligible to vote!")
    print("Make sure to bring your ID.")

print("This statement always executes.")

You are eligible to vote!
Make sure to bring your ID.
This statement always executes.

2. Discount Eligibility (condition is False)

purchase_amount = 700

if purchase_amount > 1000:
    print("You get a 10% discount!")

print("Thank you for shopping.")

Thank you for shopping.

Since purchase_amount (700) is not greater than 1000, the condition is False, so the discount message is skipped — but the "Thank you" message still prints because it lies outside the if block.

Single-Statement If (Same Line)

If the if block contains only one statement, Python allows writing it on the same line as the condition — although using a new indented line is generally preferred for readability.

age = 20
if age >= 18: print("Eligible to vote")

x = 5
if x > 10:
    print("Big")
print("Done")

Summary

The if statement evaluates a condition and runs its indented block only when that condition is True. Python relies on strict, consistent indentation instead of braces to define code blocks — omitting or misaligning it results in an IndentationError. Statements outside the block always run, regardless of the condition's outcome.