Nested Conditions (Choices Inside Choices)

In real life, making a decision often depends on a prior decision.

For example, before riding a motor bike, you must first check if you have a Driver's License. If you have a license, you then check if you are wearing a Helmet.

In Python, putting one if or if-else statement inside another if or else block is called Nested Conditions.

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1. Syntax Structure: Nested Condition in if Block

The conditional block inside another if or else block is called a Nested Conditional Block.

Syntax Structure of Nested Condition in IF Block

ifcondition_A:

INDENTATION(4 Spaces)

OUTER IF BLOCKExecutes if condition_A is True

INDENTATION

ifcondition_B:

INDENTATION(4 Spaces)

NESTED GAP(+ 4 Spaces)

NESTED CONDITIONAL BLOCKExecutes ONLY if BOTH condition_A and condition_B are True

INDENTATION

else:

INDENTATION(4 Spaces)

NESTED GAP(+ 4 Spaces)

NESTED ELSE BLOCKExecutes if condition_A is True BUT condition_B is False

Real-Time Example: Blood Donation Eligibility

age = 20
weight = 55

if age >= 18:
    print("Age requirement met.")
    
    # Nested condition inside IF
    if weight >= 50:
        print("Eligible to donate blood!")
    else:
        print("Not eligible: Weight must be 50 kg or more.")
else:
    print("Not eligible: Must be 18 years or older.")

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2. Syntax Structure: Nested Condition in else Block

We can also write a nested condition inside an else block.

Syntax Structure of Nested Condition in ELSE Block

ifcondition_A:

INDENTATION(4 Spaces)

IF BLOCK 1Executes if condition_A is True

else:

INDENTATION

ifcondition_B:

INDENTATION(4 Spaces)

NESTED GAP(+ 4 Spaces)

NESTED CONDITIONAL BLOCKExecutes if condition_A is False AND condition_B is True

Real-Time Example: Streaming Quality Check

is_logged_in = True
has_premium = False

if not is_logged_in:
    print("Please log in to watch videos.")
else:
    # Nested condition INSIDE the else block
    if has_premium:
        print("Streaming in 4K Ultra HD!")
    else:
        print("Streaming in 720p High Definition.")

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3. Best Practices for Beginners

1. Watch the Indentation: Always make sure your inner if-else blocks align properly with 4 spaces (or 8 spaces for nested blocks).
2. Keep it Simple: Try not to nest more than 2 levels deep. If code gets too deeply nested, combine rules using logical operators (and, or).

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Quick Summary

• Nested Logic: Placing an if-else statement inside the body of another if or else block.
• Indentation Hierarchy: Each level of nesting adds 4 additional indentation spaces.
• Simplification Rule: Prefer combining multiple conditions using logical operators (and, or) over deep 3+ level nesting.

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What's Next?

Now that you understand nested decisions in both if and else blocks, let's explore Match-Case Statements for handling exact pattern matches in the next lesson!