Date generator for simple backup rotation

gistfile1.py

from datetime import date, timedelta

KEEP_DAYS = 7
KEEP_WEEKS = 4
KEEP_MONTHS = 6

today = date.today()

def calculate_daily_days():
    return [today - timedelta(days=day) for day in range(0, KEEP_DAYS)]

def calculate_weekly_days():
    first_day_of_week = today - timedelta(days=today.weekday())
    return [first_day_of_week - timedelta(days=7*week) for week in range(0, KEEP_DAYS)]

def calculate_monthly_days():
    for month in range(0, KEEP_MONTHS):
        day = today.replace(day=1) # first day of this month
        for i in range(1, month+1):
            day = day - timedelta(days=1) # last day of prev month
            day = day.replace(day=1) # first day of prev month
        yield day


keep_dates =  sorted(list(set([d for d in calculate_daily_days()] + [d for d in calculate_monthly_days()] +  [d for d in calculate_weekly_days()])))
for d in keep_dates: print d