Age from Birthdate in Python

Given a birthday column, how to calculate a persons age for the current day?

• This answer assumes the desired output is the age, in years, from the birthday until today.
• (today - bd) returns a value in total number of days.
  
  • Divide by pd.Timedelta(days=365.25), to get the number of years.
    
    • 365.25 because the length of a year changes
• See Calculate Pandas DataFrame Time Difference Between Two Columns in Hours and Minutes for additional details about timedeltas and converting to different time units.
• The original function returns a value, but the returned values aren't assigned back to the dataframe, with something like df['age (years)'] = calc_age(df.birthdate), which is why the values show up in the console.
• Also, there is no need to use .apply. This applies the function iteratively, and is why there are multiple outputs to the console.

import pandas as pd
from datetime import date

# read the file in and covert the birthdate column to a datetime
df = pd.read_csv('vanco.csv', parse_dates=['birthdate'])

# function
def calc_age(bd: pd.Series) -> pd.Series:
    today = pd.to_datetime(date.today())  # convert today to a pandas datetime
    return (today - bd) / pd.Timedelta(days=365.25)  # divide by days to get years


# call function and assign the values to a new column in the dataframe
df['age (years)'] = calc_age(df.birthdate)

# display(df)
  firstname secondname  birthdate  age (years)
0     vanco     grizov 1983-03-16     37.48118
1     vlado   stojanov 1982-06-24     38.20671
2      goce     grizov 1985-07-18     35.14031

Alternatively

• Use the dateutil module, which has a more feature rich selection of methods
  
  • relativedelta will compensate for leap years
  • Use .years to extract only the year component, from the relativedelta object.

# updated function with relativedelta
def calc_age(bd: pd.Series):
    today = pd.to_datetime(date.today())
    return bd.apply(lambda x: relativedelta(today, x).years)


# function call
df['age (years)'] = calc_age(df.birthdate)

# display(df)
  firstname secondname  birthdate  age (years)
0     vanco     grizov 1983-03-16           37
1     vlado   stojanov 1982-06-24           38
2      goce     grizov 1985-07-18           35

# the output if .years is removed from the calc_age function
  firstname secondname  birthdate                                    age (years)
0     vanco     grizov 1983-03-16  relativedelta(years=+37, months=+5, days=+22)
1     vlado   stojanov 1982-06-24  relativedelta(years=+38, months=+2, days=+14)
2      goce     grizov 1985-07-18  relativedelta(years=+35, months=+1, days=+20)

Calculating Age from Birthdate TypeError: strptime() argument 1 must be str, not float

You are converting in and out of dates / datetimes a few too many times

final_df['D_O_B__c'] = pd.to_datetime(final_df['D_O_B__c'], format = "%Y-%m-%d", errors = 'coerce')
Once you've run this line, the column is now a pandas Datetime dtype

final_df['D_O_B__c'] = pd.to_datetime(final_df['D_O_B__c']).dt.date
this line is unnecessary

In the calculate age function, you don't need to use datetime.strptime since the supplied object will already be a datetime, so your function can be simplified to

def calculate_age(born):
    today = date.today()
    return today.year - born.year - ((today.month, today.day) < (born.month, born.day))

And now this line will run just fine, returning NAs for rows with bad/null timestamp strings originally

final_df['Age'] = df['D_O_B__c'].apply(calculate_age)

To fill those values in with the median age, you can just do
final_df.loc[final_df['Age'].isnull(),'Age'] = final_df['Age'].median()

which calculates the median 'Age' value for non-null rows, and then sets all null rows to that value

Calculating age in python

So close!

You need to convert the string into a datetime object before you can do calculations on it - see datetime.datetime.strptime().

For your date input, you need to do:

datetime.strptime(input_text, "%d %m %Y")

#!/usr/bin/env python3

from datetime import datetime, date

print("Your date of birth (dd mm yyyy)")
date_of_birth = datetime.strptime(input("--->"), "%d %m %Y")

def calculate_age(born):
    today = date.today()
    return today.year - born.year - ((today.month, today.day) < (born.month, born.day))

age = calculate_age(date_of_birth)

print(age)

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PS: I urge you to use a sensible order of input - dd mm yyyy or the ISO standard yyyy mm dd

how to calculate age form list of dates in python

You will need to format the dates appropriately, so research the datetime date function and figure out where to go from here.

from datetime import date
today = date.today()

for n, bday in zip(name, birthdate):
  age = (today - date(bday)).years
  print("Student ", n, "age is ", age, "years old.")

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

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

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