Set Airflow data interval to cover the previous month

How to set the Airflow data interval to start at the start of the previous month and to end on the end of the previous month?

Let's suppose that I have an ETL process that is executed at 8:00 a.m. on the 7th day of each month. I want to transform new data that were inserted between the start and end of the previous month.

So:

• on March 7th I want to process the data that arrived between Feb 1 and Feb 28 (or 29),
• on April 7th I want to process the data that arrived between Mar 1 and Mar 31,
• etc.

Unfortunately, I haven't found the way to "shift" the data interval so that it starts on the first and ends on the last day of the previous month.
Currently, if I execute the DAG, I will get following the period:

• for March 7th: 2023-02-07 8:00 a.m. - 2023-03-03 8:00 a.m.

from __future__ import annotations
from datetime import datetime
from airflow import DAG
from airflow.operators.python import PythonOperator
from airflow.timetables.interval import CronDataIntervalTimetable

##############


def do_the_etl(start_date_str: str, end_date_str: str) -> None:
    """
    in reality this executes a lenghty etl process,
    here just print a message
    """

    start_date = datetime.fromisoformat(start_date_str)
    end_date = datetime.fromisoformat(end_date_str)

    print(f"[Fake ETL] Querying for the period {start_date}-{end_date}")


####

ETL_DATE_START = "{{ data_interval_start }}"
ETL_DATE_END = "{{ data_interval_end }}"

##############

with DAG(
    dag_id="etl_test",
    start_date=datetime(2023, 2, 4),
    schedule_interval=CronDataIntervalTimetable(cron="0 8 7 * *", timezone="Etc/UTC"),
    catchup=False,
) as dag:
    run_etl = PythonOperator(
        task_id="etl",
        python_callable=do_the_etl,
        op_kwargs={
            "start_date_str": ETL_DATE_START,
            "end_date_str": ETL_DATE_END,
        },
    )

    run_etl

You can use relativedelta to modify the date.

# interval_start
{{ data_interval_end + macros.dateutil.relativedelta.relativedelta(months=-1, day=1) }}
# interval_end
{{ data_interval_end + macros.dateutil.relativedelta.relativedelta(months=-1, day=31) }}

months=-1 means subtracting one month from the date.

day=1 means setting the day of the date as 1. Note it's not days.

day=31 means setting the day of the date as the last day regardless of number of days in the month.