return first and last day of a month (in datetime)

first_last_day.py

from datetime import datetime, timedelta, date

def get_first_day(dt, d_years=0, d_months=0):
    # d_years, d_months are "deltas" to apply to dt
    y, m = dt.year + d_years, dt.month + d_months
    a, m = divmod(m - 1, 12)
    dt = date(y + a, m + 1, 1)
    return datetime(dt.year, dt.month, dt.day, 0, 0, 0)

def get_last_day(dt):
    dt = get_first_day(dt, 0, 1) + timedelta(-1)
    return datetime(dt.year, dt.month, dt.day, 23, 59, 59)