python获取当前时间的前一天，前一周，前一个月

import datetime

d = datetime.datetime.now()

def day_get(d):
    oneday = datetime.timedelta(days=1)
    day = d - oneday
    date_from = datetime.datetime(day.year, day.month, day.day, 0, 0, 0)
    date_to = datetime.datetime(day.year, day.month, day.day, 23, 59, 59)
    print '---'.join([str(date_from), str(date_to)])

def week_get(d):
    dayscount = datetime.timedelta(days=d.isoweekday())
    dayto = d - dayscount
    sixdays = datetime.timedelta(days=6)
    dayfrom = dayto - sixdays
    date_from = datetime.datetime(dayfrom.year, dayfrom.month, dayfrom.day, 0, 0, 0)
    date_to = datetime.datetime(dayto.year, dayto.month, dayto.day, 23, 59, 59)
    print '---'.join([str(date_from), str(date_to)])

def month_get(d):
    dayscount = datetime.timedelta(days=d.day)
    dayto = d - dayscount
    date_from = datetime.datetime(dayto.year, dayto.month, 1, 0, 0, 0)
    date_to = datetime.datetime(dayto.year, dayto.month, dayto.day, 23, 59, 59)
    print '---'.join([str(date_from), str(date_to)])

转载自http://www.oschina.net/code/snippet_736230_26816