? Python If Else

? Quick Overview

Conditional statements in Python let your program make decisions based on conditions. The main keywords are if, elif, and else.

if runs a block when the condition is true.
elif lets you check more conditions if the previous ones are false.
else runs a block when all previous conditions are false.
You can also nest if statements to handle more complex decisions.

? Key Concepts

Condition: An expression that evaluates to True or False.
Indentation: Defines which statements belong to which block in Python.
If-Else flow: Only one branch of an if–elif–else chain runs.
Nested if: An if statement inside another if for detailed checks.

? Syntax and Flow

Basic if syntax:

? View If Syntax

if condition:
    # block of code
    statement1
    statement2

if–else syntax:

? View If-Else Syntax

if condition:
    # block if condition is True
    statement1
else:
    # block if condition is False
    statement2

if–elif–else chain syntax:

? View If-Elif-Else Syntax

if condition1:
    # runs if condition1 is True
    statement_block_1
elif condition2:
    # runs if condition2 is True
    statement_block_2
elif condition3:
    # runs if condition3 is True
    statement_block_3
else:
    # runs if all conditions above are False
    default_statement_block

Nested if syntax:

? View Nested If Syntax

if outer_condition:
    # outer block
    if inner_condition:
        # inner block
        statement_block_inner
    else:
        statement_block_inner_else
else:
    statement_block_outer_else

? Code Examples

⚡ Basic If Statement

The if statement allows you to execute a block of code only if a condition is true.

? View Code Example

age = 18
# Check if the person is an adult
if age >= 18:
    print("You are an adult.")

In this example, the message is printed only if the condition age >= 18 is true.

? If-Else Statement

The else clause allows you to execute a block of code if the if condition is false.

? View Code Example

age = 16
# Decide if the person is an adult or a minor
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

? Elif (Else If) Statement

The elif statement allows you to check multiple conditions in sequence.

? View Code Example

score = 85
# Choose the grade based on the score
if score >= 90:
    print("Grade A")
elif score >= 75:
    print("Grade B")
else:
    print("Grade C")

Here, Python checks the if condition first. If false, it checks elif, and finally else if all conditions are false.

? Nested If Statements

You can also nest if statements inside another if statement for more complex conditions.

? View Code Example

num = 15
# Check if the number is positive and whether it is even or odd
if num > 0:
    if num % 2 == 0:
        print("Positive Even Number")
    else:
        print("Positive Odd Number")
else:
    print("Non-positive Number")

? Live Output & Explanation

Basic If (age = 18) → condition age >= 18 is True, so it prints:
You are an adult.
If-Else (age = 16) → condition age >= 18 is False, so the else block runs and prints:
You are a minor.
Elif (score = 85) → first condition score >= 90 is False, second condition score >= 75 is True, so it prints:
Grade B
Nested If (num = 15) → num > 0 is True, so we go inside:
- num % 2 == 0 is False, so the inner else runs and prints:
  Positive Odd Number

? Tips & Best Practices

Use if for simple conditional checks.
Use elif for multiple conditions instead of writing many separate if blocks.
Use nested if statements for complex logic that depends on previous checks.
Indentation is critical in Python; each block must be properly indented with the same number of spaces.
Keep conditions simple and readable; you can store them in variables if they get too long.

? Try It Yourself

Write a program to check if a number is positive, negative, or zero using if-elif-else.
Write a program to check if a person is a child, teen, or adult based on age.
Use nested if to check if a number is even and positive.
Modify the grade example to include more ranges like A+, B+, and so on.