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30. Nested Conditionals

1. Introduction​

A nested conditional is an if statement inside another if.
They let you check conditions within conditions, useful when decisions depend on multiple factors.

2. Basic Nested if​

age = 20
has_id = True

if age >= 18:
    if has_id:
        print("Access granted")

3. Nested if-else​

x = 15

if x > 0:
    if x % 2 == 0:
        print("Positive even number")
    else:
        print("Positive odd number")
else:
    print("Not a positive number")

4. Multiple Levels of Nesting​

You can nest deeper, but code becomes harder to read.

x = 12

if x > 0:
    if x < 20:
        if x % 3 == 0:
            print("Positive number < 20 and divisible by 3")

5. Combining Conditions Instead​

Often you can avoid deep nesting with logical operators.

❌ Nested:

if age >= 18:
    if has_ticket:
        print("Welcome")

✅ Better:

if age >= 18 and has_ticket:
    print("Welcome")

6. When Nested Conditionals are Useful​

  • Complex decision-making where one condition depends on another.
  • Validating multiple layers of requirements (e.g., login + role check).
  • When clarity is better served by nesting than by a long combined condition.

7. Common Mistakes​

  • Too many nested levels → code becomes unreadable.
  • Forgetting to properly indent nested blocks.
  • Overusing nesting where elif or logical operators would be simpler.

8. Practical Example​

username = "admin"
password = "secret"

if username == "admin":
    if password == "secret":
        print("Login successful")
    else:
        print("Wrong password")
else:
    print("Unknown user")

9. Best Practices​

  • Limit nesting to 2–3 levels maximum.
  • Refactor deeply nested conditionals into functions.
  • Use elif or compound conditions for clarity when possible.

10. Next Steps​

✅ You now understand nested conditionals and when to use them.
In the next chapter, we’ll explore while loops, which allow repeating actions while a condition is true.