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29. elif and else

1. Introduction​

The if statement checks a single condition.
But in real programs, you often need to check multiple possibilities.
That’s where elif (else if) and else come in.

2. The else Clause​

else runs when all previous conditions are false.

age = 16

if age >= 18:
    print("You are an adult")
else:
    print("You are a minor")

Output:

You are a minor

3. The elif Clause​

elif lets you check additional conditions.

score = 85

if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Output:

Grade: B

4. Multiple elif Clauses​

You can chain as many elif clauses as needed, but only one else.

temperature = 25

if temperature > 30:
    print("Hot")
elif temperature > 20:
    print("Warm")
elif temperature > 10:
    print("Cool")
else:
    print("Cold")

5. Order of Conditions Matters​

Python checks conditions top to bottom.
As soon as one condition is true, the rest are ignored.

x = 15

if x > 10:
    print("Greater than 10")
elif x > 5:
    print("Greater than 5")

Output:

Greater than 10

6. Nested Conditionals vs elif​

Instead of multiple nested if statements, elif makes code cleaner.

❌ Nested:

x = 10
if x >= 0:
    if x == 0:
        print("Zero")
    else:
        print("Positive")

✅ Better:

x = 10
if x < 0:
    print("Negative")
elif x == 0:
    print("Zero")
else:
    print("Positive")

7. Using Boolean Operators with if​

You can combine conditions using and, or, and not.

age = 20
has_id = True

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

8. Short-Circuiting​

Python stops evaluating conditions as soon as the result is known.

x = 0

# This won't cause ZeroDivisionError
if x != 0 and (10 / x > 1):
    print("Condition met")

Here, since x != 0 is False, Python never checks the second condition.

9. Membership Tests in Conditions​

You can use in and not in directly.

fruits = ["apple", "banana", "cherry"]

if "apple" in fruits:
    print("Apple found")
elif "orange" not in fruits:
    print("No orange here")

10. Conditional Expressions (Ternary Operator)​

Python has a compact way to write if-else inside an expression:

age = 18
status = "adult" if age >= 18 else "minor"
print(status)  # adult

11. Common Beginner Mistakes​

  • Forgetting the colon (:): 
    if x > 5   # ❌ SyntaxError
  • Using = instead of ==: 
    if x = 5:  # ❌ invalid
  • Misordering conditions: 
    if x > 0:
        print("Positive")
    elif x > 10:   # ❌ unreachable, since >10 is already >0
        print("Greater than 10")

12. Best Practices​

  • Keep conditions simple and readable.
  • Avoid deep nesting; prefer elif.
  • Use parentheses in complex conditions for clarity.
  • If multiple conditions lead to the same action, group them with or.

13. Practical Example​

marks = 72

if marks >= 90:
    grade = "A"
elif marks >= 75:
    grade = "B"
elif marks >= 50:
    grade = "C"
else:
    grade = "F"

print("Your grade is", grade)

14. Next Steps​

✅ You now understand how to use elif and else, along with advanced condition-handling techniques.
In the next chapter, we’ll look at nested conditionals in more detail.