Python relativedelta to get duration of difference between two date objects

Importing datetime library

from dateutil.relativedelta import relativedelta

Watch difference between day and days


# day and days
from dateutil.relativedelta import relativedelta
from datetime import date

dt = date.today()  # today is 2019-09-23

# Adding one day to today
print(dt + relativedelta(days=1))  # 2019-09-24

# 1st day of the month
print(dt + relativedelta(day=1))  # 2019-09-01

relativedelta(year,month,day, hour,minute, second, microsecond)

Note : Here all arguments are singular, we will check by using both. Here is the code.

from dateutil.relativedelta import relativedelta
dt = relativedelta(year=2021, month=1, day=1,hour=23,minute=56,second=57, microsecond=324534)
print(dt)
print(dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, dt.microsecond)

Output

relativedelta(year=2021, month=1, day=1, hour=23, minute=56, second=57, microsecond=324534)
2021 1 1 23 56 57 324534

We will use plurals now. This will add the arguments to our date object.

from dateutil.relativedelta import relativedelta

dt = relativedelta(years=1, months=2, days=3, hours=23, minutes=56, 
    seconds=57, microseconds=324534)

from datetime import date
dt_today = date.today()  # today is 2019-09-23
print(dt_today + dt)

Output

2020-11-26 23:56:57.324534

Using datetime ( adding to current date and time )

from dateutil.relativedelta import relativedelta

dt = relativedelta(
    years=1, 
    months=2, 
    days=3, 
    hours=23, 
    minutes=56, 
    seconds=57, 
    microseconds=324534
)

from datetime import datetime

dt_now = datetime.now()

print(dt_now)
print(dt_now + dt)

Output

2019-09-23 14:48:35.124959
2020-11-27 14:45:32.449493

Here are some common uses of relativedelta to find out date and time remaining or to apply any datetime calculation

Number of Month and days left for New Year

from dateutil.relativedelta import relativedelta
from datetime import date

dt = date.today()

print("Today:", dt)

print("No of days left for New year")

dt2 = date(dt.year + 1, 1, 1)

dt3 = relativedelta(dt2, dt)

print(
    "Days:", dt3.days, 
    "Months:", dt3.months, 
    "Years:", dt3.years
)

Output

Today: 2019-09-21
No of days left for New year
Days: 11  
Months: 3  
Years: 0

Countdown ( Hour : Minute : Seconds ) for new year and showing Message

Age Calculation

Input date of birth in Year, Month , day format. Output saying year month and days.

from dateutil.relativedelta import relativedelta
from datetime import date

dt = date.today()
dob = date(1996, 5, 15)  # date of birth as Year, month, day

dt3 = relativedelta(dt, dob)

print(
    "Days:", dt3.days, 
    "Months:", dt3.months, 
    "Years:", dt3.years
)

Output

Days: 16  Months: 3  Years: 25

Adding a month to any date

We will findout difference between relativedelta and timedelta
Let us take the 31^st of Jan 2019 as our date and we will add one month to this date.

By using month part of date object

from datetime import date

print("Adding 1 month to 31st of Jan")

dt1 = date(2019, 1, 31)

dt3 = date(
    dt1.year, 
    dt1.month + 1, 
    dt1.day
)  # ValueError generated

print(dt3)

This will generate ValueError and say day is out of range for month

By using timedelta
As there is no Month attribute for our timedelta, we can add 30 days

from datetime import timedelta, date, datetime

dt1 = date(2019, 1, 31)
dt3 = dt1 + timedelta(days=30)
print(dt3)  # 2019-03-02

dt1 = date(2020, 1, 31)
dt3 = dt1 + timedelta(days=30)
print(dt3)  # 2020-03-01

However you can see it takes care of leap year
By using relativedelta

from dateutil.relativedelta import relativedelta
from datetime import date

dt1 = date(2019, 1, 31)
dt3 = dt1 + relativedelta(months=1)
print(dt3)  # 2019-02-28

dt1 = date(2020, 1, 31)  # Leap year
dt3 = dt1 + relativedelta(months=1)
print(dt3)  # 2020-02-29

This gives us the last day of Feb month and at the same time takes care of leap year. relativedelta is usefull in handling adding or subtracting months , years etc.

Example 2: Adding Months and Days

from datetime import datetime
from dateutil.relativedelta import relativedelta

today = datetime.now()  # today's date used

new_date = today + relativedelta(months=3, days=5)

print(new_date)

Example 3: Subtracting Years and Weeks

new_date = today - relativedelta(years=2, weeks=1)
print(new_date)

Adding sequence

relativedelta is added to a datetime in the following sequence.

Year
Month
Day
Hours
Minutes
Seconds
Microsecond

After adding the relativedelta we will apply the weekdays.

from dateutil.relativedelta import relativedelta
from datetime import date
from dateutil.rrule import MO, TU, WE, TH, FR, SA, SU

dt = date.today()  # today is 2019-09-22

# 2nd Monday from today
print(dt + relativedelta(weekday=MO(2)))  # 2019-09-30

# 2nd Monday of present Month
print(dt + relativedelta(day=1, weekday=MO(2)))  # 2019-09-09

# Next Sunday from today
print(dt + relativedelta(weekday=SU(+1)))  # 2019-09-22

# As today is Sunday there is no difference with SU(+1) or SU(-1)
print(dt + relativedelta(weekday=SU(-1)))  # 2019-09-22

# Previous 2nd Tuesday
print(dt + relativedelta(weekday=TU(-2)))  # 2019-09-10

All Date Objects All timedelta objects

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	23-07-2020
Thanks for this tutorial was really helpful...

	26-11-2020
Very helpful especially the rrule entry.