Calculates the first and the last day of previous datetime month.

last_month_range.py

from datetime import datetime
import calendar

def calc_last_month_range(date: datetime) -> tuple:
    if date.month == 1:
        ini_date = datetime(date.year - 1, 12, 1)
    else:
        ini_date = datetime(date.year, date.month - 1, 1)

    end_date = datetime(
        ini_date.year,
        ini_date.month,
        calendar.monthrange(ini_date.year, ini_date.month)[1],
    )

    return ini_date, end_date