Nested Conditional Statements in Python

In Python, a nested conditional is when one if statement is placed inside another if statement. This allows for more complex decision-making processes, where a condition is only checked if a previous condition was satisfied. Nested conditionals can be powerful but should be used with caution, as they can make the code harder to read and maintain.

Syntax:

Syntax of Nested Conditional

if condition1:
    if condition2:
        # Block of code if both condition1 and condition2 are True
    else:
        # Block of code if condition1 is True but condition2 is False
else:
    # Block of code if condition1 is False

How It Works:

• condition1 is evaluated first.
• If condition1 is True, the program enters the inner block and evaluates condition2.
• If condition2 is also True, the corresponding code is executed.
• If condition1 is False, the program skips the entire block of code and moves to the else block (if present).

Example 1: Voting Eligibility and Age Restriction

Let’s take an example where we check if a person is eligible to vote, and if they are eligible, we check if they are old enough to drink alcohol.

Voting Eligibility and Age Restriction

age = 20

if age >= 18:
    print("You are eligible to vote.")
    if age >= 21:
        print("You are also old enough to drink alcohol.")
    else:
        print("But you are not old enough to drink alcohol.")
else:
    print("You are too young to vote.")

Explanation:

• The outer if checks if the person is 18 or older.
• If age >= 18 is True, the program enters the nested if block and checks if the person is oldenough to drink.
• If the person is 21 or older, the message about drinking alcohol is printed; otherwise, the else statement within the nested block handles the case where they can’t drink alcohol.

Example 2: Number Category

In this example, we will check if a number is positive, negative, or zero, and if it’s positive, we’ll further categorize it as small or large.

Number Category

number = 50

if number > 0:
    print("The number is positive.")
    if number < 100:
        print("It’s a small number.")
    else:
        print("It’s a large number.")
elif number == 0:
    print("The number is zero.")
else:
    print("The number is negative.")

Explanation:

• The outer if checks if the number is positive.
• If it is positive, we then check whether it’s smaller than 100 or larger.
• If the number isn’t positive, we use an elif to check if it is zero, and the else block handles the case where the number is negative.

Exercise: Nested Conditional Statements

1. Write a program that takes the temperature as input and does the following:

   • If the temperature is below 0, print “It’s freezing.”
   • If the temperature is above 0, check if it’s above 30:
     • If it’s above 30, print “It’s hot.”
     • Otherwise, print “It’s a mild day.”

2. Write a program that calculates the discount based on the total purchase:

   • If the purchase amount is greater than $100, apply a 10% discount.
   • If the purchase amount is greater than $200, apply an additional 5% discount (making it 15% total).
   • If the purchase is less than $100, no discount is applied.