Leap Year Program in Python

The question

Read a year and print Leap year or Not a leap year. A year is a leap year if it is divisible by 4 but not by 100, or if it is divisible by 400.

The code

y = int(input())
if (y % 4 == 0 and y % 100 != 0) or y % 400 == 0:
    print("Leap year")
else:
    print("Not a leap year")

How it works

1. 1A year divisible by 4 is usually a leap year…
2. 2…except century years (divisible by 100), which are not…
3. 3…unless they are also divisible by 400. So 2000 is a leap year but 1900 is not.
4. 4All three rules fit in one condition: (y % 4 == 0 and y % 100 != 0) or y % 400 == 0.

The condition on four years

1900 is the trap: it divides by 4 and by 100 but not by 400, so it is not a leap year.

Leap year program using nested if

The three rules written one inside the other, in the order you would say them aloud. Longer, but easy to explain in a viva.

y = int(input())
if y % 4 == 0:
    if y % 100 == 0:
        if y % 400 == 0:
            print("Leap year")
        else:
            print("Not a leap year")
    else:
        print("Leap year")
else:
    print("Not a leap year")

1900

Not a leap year

Leap year using the calendar module

Python already knows the rule: calendar.isleap() returns True or False. Fine for real programs; in an exam, write the condition yourself unless the question allows a module.

import calendar

y = int(input())
if calendar.isleap(y):
    print("Leap year")
else:
    print("Not a leap year")

2000

Leap year

Leap year in Python using a function

Return the condition itself — it is already True or False. Then the same function can check a whole list of years.

def is_leap(y):
    return (y % 4 == 0 and y % 100 != 0) or y % 400 == 0

for y in [1900, 2000, 2023, 2024]:
    print(y, is_leap(y))

(no input)

1900 False
2000 True
2023 False
2024 True

Questions students ask

What is the condition for a leap year in Python?

(y % 4 == 0 and y % 100 != 0) or y % 400 == 0. A year is a leap year when it divides by 4 but not by 100, or when it divides by 400.

Is 1900 a leap year? Is 2000?

1900 is not: it divides by 100 but not by 400. 2000 is: it divides by 400. 2024 and 2028 are leap years; 2100 will not be.

More in if / else

• Python Program to Check Even or Odd Number
• Python Program to Find the Largest of Three Numbers
• Python Program to Check Vowel or Consonant