# How to compute number of days in a year in Python using Pendulum

Also see How to compute number of days in a year in Pandas

We can use the excellent `pendulum`

library to find the number of days in a given year

```
import pendulum
def number_of_days_in_year(year):
start = pendulum.date(year, 1, 1)
end = start.add(years=1)
return (end - start).in_days()
```

#### Usage example:

```
print(number_of_days_in_year(2020)) # Prints 366
print(number_of_days_in_year(2021)) # Prints 365
```

#### Explanation:

First, we define the `start`

date to be the first day (1st of January) of the year we’re interested in:

```
start = pendulum.date(year, 1, 1)
```

Now we use `pendulum`

‘s `add`

function to add exactly one year to that date. This will always result in the 1st of January of the year after the given year:

```
end = start.add(years=1)
```

The rest is simple: Just ask `pendulum`

to give us the number of days in the difference between `end`

and `start`

:

```
(end - start).in_days()
```