Obtaining N Months Ago in Python's datetime Without Using dateutil

Here is the English translation of the provided Japanese blog article:

Function to Get N Months Ago in datetime Without Using dateutil

Since dateutil was not available in the Python Data Source of Re:dash, I created this function.

import datetime

def previous_month(dt, delta_months=1):
    """
    Get the date n months ago in datetime.
    
    Normally, dateutil would be used, but this code is for environments where dateutil cannot be used.
    """
    if delta_months == 0:
        return dt
    new_dt = datetime.datetime(dt.year, dt.month, 1) \
             - datetime.timedelta(days=1)
    return previous_month(datetime.datetime(
        new_dt.year, new_dt.month, 1), delta_months - 1)

for i in range(13):
    print(
        f'2022-02-10 - {i} =>',
        previous_month(datetime.datetime(2022, 2, 10), i))

Results

2022-02-10 - 0 => 2022-02-10 00:00:00
2022-02-10 - 1 => 2022-01-01 00:00:00
2022-02-10 - 2 => 2021-12-01 00:00:00
2022-02-10 - 3 => 2021-11-01 00:00:00
2022-02-10 - 4 => 2021-10-01 00:00:00
2022-02-10 - 5 => 2021-09-01 00:00:00
2022-02-10 - 6 => 2021-08-01 00:00:00
2022-02-10 - 7 => 2021-07-01 00:00:00
2022-02-10 - 8 => 2021-06-01 00:00:00
2022-02-10 - 9 => 2021-05-01 00:00:00
2022-02-10 - 10 => 2021-04-01 00:00:00
2022-02-10 - 11 => 2021-03-01 00:00:00
2022-02-10 - 12 => 2021-02-01 00:00:00

Addendum: Modified Because Recursive Call Was Not Possible in Redash

def previous_month(dt, delta_months=1):
    """
    Get the date n months ago in datetime.

    Normally, dateutil would be used, but this code is for environments where dateutil cannot be used.
    """
    import datetime
    new_dt = datetime.datetime(dt.year, dt.month, 1)
    for i in range(delta_months):
        new_dt = new_dt - datetime.timedelta(days=1)
        new_dt = datetime.datetime(new_dt.year, new_dt.month, 1)
    return new_dt