Python: Increasing Dates with each Loop

Question

For a current project, I am planning to increase the value of a calendar date by 3 months with each iteration/loop. The value for start_date should hence be [1st iteration]: 01/01/2017, [2nd interation] 01/04/2017 etc. For end_date, it should accordingly yield [1st iteration]: 31/03/2017, [2nd interation] 30/06/2017 etc.

I originally thought it would be a simple point to solve but somehow the script is not working as planned (also as many threads discuss how to increase values in one go but not how to perform this in several loops). Does anyone know how to tweak things?

The corresponding code looks as follows:

import datetime
from dateutil.relativedelta import *

for i in df.iterrows():
    start_date = '01/01/2017'
    start_date = start_date + relativedelta(months=+3)
    end_date = '31/03/2017'
    end_date = end_date + relativedelta(months=+3)

    print(start_date)
    print(end_date)

David · Accepted Answer · 2020-05-17 19:38:34Z

1

Your problem is that you are initialising the start_date and end_date inside the loop. Just initialise them once outside the loop, then continue process like you're doing.

import datetime
from dateutil.relativedelta import *

# year, month, day
start_date = datetime.date(2017, 1, 1)
end_date = datetime.date(2017, 3, 31)

for i in df.iterrows():
    start_date += relativedelta(months=3)
    end_date += relativedelta(months=3)

    print(start_date)
    print(end_date)

edited May 17, 2020 at 19:38

answered May 17, 2020 at 19:27

David

1,2105 gold badges14 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

Malte Susen Over a year ago

Thanks for this. It is yielding the error start_date = start_date + relativedelta(months=+3) - TypeError: can only concatenate str (not "relativedelta") to str though. Let me figure out how this can be solved.

David Over a year ago

See my edit. Parsing the values as dates should get the job done.

David Over a year ago

Yep, my mistake. You have to remove the zeros. Also, make sure you have the day and month in the correct order.

David Over a year ago

hmm, that's strange. Works for me. Maybe try: datetime.date.fromisoformat('2017-01-01').

David Over a year ago

Glad I helped :) Cheers.

|

Collectives™ on Stack Overflow

Python: Increasing Dates with each Loop

1 Answer 1

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related