How to get the first day of the previous month using Python?

first-day-of-previous-month.md

How to get the first day of the previous month using Python?

Using datetime

from datetime import date

d = date(2019, 1, 8)  # date.today()

month, year = (d.month-1, d.year) if d.month != 1 else (12, d.year-1)

last_month = d.replace(day=1, month=month, year=year)

print(last_month)  # 2018-12-01

Using datetime and timedelta

from datetime import date
from datetime import timedelta

d = date(2019, 1, 8)  # date.today()

last_month = (d - timedelta(days=d.day)).replace(day=1)

print(last_month)  # 2018-12-01

Using dateutil

from datetime import date
from dateutil.relativedelta import relativedelta

d = date(2019, 1, 8)  # date.today()

last_month = d.replace(day=1) - relativedelta(months=1)

print(last_month)  # 2018-12-01

Using arrow

import arrow

d = arrow.get(2019, 1, 8)  # arrow.now()

last_month = d.shift(months=-1).replace(day=1).datetime.date()

print(last_month)  # 2018-12-01