if-elif-else Statements

if-elif-else Statements#

Note

Source: Adapted from the C# edition (decisions/ifelsechained.rst). The grade-classification and wages examples are Python adaptations of the original C# examples. The BMI and ticket-price examples are original additions.

When there are more than two choices, chain conditions using elif (short for “else if”). Python uses elif where C# uses else if.

Grade Classification#

score = int(input("Enter score (0-100): "))
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"
print(f"Grade: {grade}")

Python evaluates the conditions top to bottom and executes the first block whose condition is True. Once a branch runs, the rest are skipped. The else at the end is a catch-all — it runs only when none of the earlier conditions were true.

Note

The conditions above are ordered from highest to lowest. Because we already know score < 90 by the time we test score >= 80, there is no need to write 80 <= score < 90. Each elif implicitly carries the negation of all previous conditions.

General Form#

if condition1:
    statements
elif condition2:
    statements
elif condition3:
    statements
...
else:
    statements

Any number of elif clauses is allowed. The else clause is optional but good practice when one of the choices should always apply.

Wages with Overtime#

def weekly_wages(hours, rate):
    """Return total weekly wages including 1.5x overtime above 40 hours."""
    if hours <= 40:
        return hours * rate
    else:
        overtime = hours - 40
        return 40 * rate + overtime * rate * 1.5

hours = float(input("Hours worked: "))
rate  = float(input("Hourly rate: $"))
pay   = weekly_wages(hours, rate)
print(f"Weekly wages: ${pay:.2f}")

Sample run:

Hours worked: 45
Hourly rate: $20
Weekly wages: $950.00

BMI Categories#

Here is an example with four elif branches:

def bmi_category(bmi):
    """Return the weight category for a given BMI."""
    if bmi < 18.5:
        return "Underweight"
    elif bmi < 25.0:
        return "Normal"
    elif bmi < 30.0:
        return "Overweight"
    else:
        return "Obese"

bmi = float(input("Enter BMI: "))
print(bmi_category(bmi))

if-elif-else Exercise#

Write a function ticket_price(age) that returns the ticket price based on the following rules:

  • Under 5: free (0)

  • 5–12: $8

  • 13–64: $15

  • 65 and over: $10

Test it with ages 3, 10, 30, and 70.