Given that we are in a leap year this year (2020), it would be nice to know how to programmatically calculate this.

Luckily, this is a repeatable pattern that we can write some code for.

## So what is a leap year?

A `leap year`

is a year that has 29 days in the month of February.

Astronomical years have a quarter of a day more than our calendar years that we follow, so to make sure this matches up continually, our calendar introduces an additional day every 4 years.

## Building a pattern

The pattern we can follow to make sure that we write our code correctly is:

Ifthe year is not divisible by 4thenit is a common yearElse ifthe year is not divisible by 100thenit is a leap yearElse ifthe year is not divisible by 400thenit is a common yearElse itis a leap year

## Writing some code

We can easily turn this into code:

def isLeapYear(year): if year % 4 != 0: return False, "Common year" elif year % 100 != 0: return True, "Leap year" elif year % 400 != 0: return False, "Common year" else: return True, "Leap year"

Our function above takes in a `year`

variable and returns two variables. A `boolean`

is it is a leap year or not and a `string`

telling us what it is.

## Testing our code

Let’s test it!

print( isLeapYear(2020) ) # (True, 'Leap year') print( isLeapYear(1999) ) # (False, 'Common year') print( isLeapYear(1685) ) # (False, 'Common year')