How to get a person's age from his date of birth in Odoo?

Question

In my module I have an entity "Person" with two fields "date_of_birth" (Date) and "age" (Integer). How can I get the age of a Person from the date of birth and give that value to the age field?

Answer 1

Dates are complicated. If you subtract two dates from each other (assuming datetime.date) you get a timedelta consisting of a number of days. Because of leap years you can't reliably calculate number of years from that. By dividing by 365.25, you get a number of years that's correct in most cases. But most cases is usually not acceptable.

Instead, you should calculate year difference, offset by -1 if the person has not had their birthday in the current year.

from datetime import date

def get_age(date_of_birth: date) -> int:
    today = date.today()
    offset = int(date_of_birth.replace(year=today.year) > today)  # int(True) == 1, int(False) == 0
    return date.today().year - date_of_birth.year - offset

Tests

# On 2020-05-11
get_age(date(2020, 5, 11))
>>> 0
get_age(date(2020, 5, 12))
>>> -1
get_age(date(2000, 5, 11))
>>> 20
get_age(date(2000, 5, 12))
>>> 19