Ternary operator

Année bissextile
Année bissextile dans le parcours Python 
def leap_year(year):
    return not year % 400 if not year % 100 else not year % 4

A ternary operator uses a maximum of two checks to determine if a year is a leap year.

It starts by testing the outlier condition of the year being evenly divisible by 100. It does this by using the modulo operator. Also, by using the falsiness of 0, the not operator can be used instead of comparing equality to 0.

  • If the year is evenly divisible by 100, then the ternary operator returns True if the year is evenly divisible by 400.
  • If the year is not evenly divisible by 100, the ternary operator returns True if the year is evenly divisible by 4.
year year % 100 == 0 year % 400 == 0 year % 4 == 0 is leap year
2020 False not evaluated True True
2019 False not evaluated False False
2000 True True not evaluated True
1900 True False not evaluated False

Although it uses a maximum of only two checks, the ternary operator tests an outlier condition first, making it less efficient than the boolean chain approach that first tests if the year is evenly divisible by 4 (which is more likely than the year being evenly divisible by 100). The ternary operator was fastest in benchmarking when the year was a leap year or was evenly divisible by 100, but those are the least likely conditions.

23e Sep 2026 · Tu l'as trouvée utile ?

Autres approches pour l'exercice Année bissextile dans le parcours Python

D'autres façons dont notre communauté a résolu cet exercice
def leap_year(year):
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)
Boolean chain

Use a chain of boolean expressions. 

from datetime import datetime, timedelta


def leap_year(year):
    return (datetime(year, 2, 28) + timedelta(days=1)).day == 29
datetime addition

Use datetime addition. 

from calendar import isleap

def leap_year(year):
    return isleap(year)
calendar.isleap() function

Use the calendar module.