Conditional Statements in Python

Conditional statements are used to make decisions in a Python program.

They allow a program to execute different blocks of code depending on whether a condition is True or False.

Types of Conditional Statements

Python provides the following conditional statements:

1. if
2. if...else
3. if...elif...else
4. Nested if

1. The if Statement

The if statement executes a block of code only when the given condition is True.

Syntax

if condition:
    # code to execute

Example

age = 18

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

Output:

You are eligible to vote

2. The if...else Statement

The else block executes when the if condition is False.

Syntax

if condition:
    # code if condition is True
else:
    # code if condition is False

Example

age = 16

if age >= 18:
    print("You are eligible to vote")
else:
    print("You are not eligible to vote")

Output:

You are not eligible to vote

3. The if...elif...else Statement

When you need to check multiple conditions, you can use elif.

Syntax

if condition1:
    # code
elif condition2:
    # code
else:
    # code

Example

marks = 75

if marks >= 90:
    print("Grade A+")
elif marks >= 75:
    print("Grade A")
elif marks >= 60:
    print("Grade B")
else:
    print("Grade C")

Output:

Grade A

4. Nested if Statement

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

Example

age = 20
has_id = True

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

Output:

Entry allowed

Using Comparison Operators

Conditional statements commonly use comparison operators.

Example

a = 10
b = 20

if a < b:
    print("a is smaller than b")

Output:

a is smaller than b

Using Logical Operators

You can combine multiple conditions using logical operators.

and

Returns True when both conditions are true.

age = 25
salary = 30000

if age >= 18 and salary >= 25000:
    print("Eligible")

or

Returns True when at least one condition is true.

age = 17
has_permission = True

if age >= 18 or has_permission:
    print("Allowed")

not

Reverses the result of a condition.

is_raining = False

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

Important: Indentation

Python uses indentation to define a block of code.

Correct:

age = 20

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

Incorrect:

age = 20

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

The second example produces an IndentationError.

Real-World Example

username = "admin"
password = "1234"

if username == "admin" and password == "1234":
    print("Login successful")
else:
    print("Invalid username or password")

Output:

Login successful

Summary

Conditional statements allow Python programs to make decisions.

The main conditional statements are:

if
if...else
if...elif...else
nested if

They are essential for controlling the flow of a Python program.

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