python——计算上周5的日期

第一种方法：

Python代码

from datetime import datetime, timedelta

weekdays = ['Monday','Tuesday','Wednesday','Thursday',

'Friday','Saturday','Sunday']

def get_previous_byday(dayname, start_date=None):

if start_date is None:

start_date = datetime.today()

day_num = start_date.weekday()

day_num_target = weekdays.index(dayname)

days_ago = (7 + day_num - day_num_target) % 7

if days_ago == 0:

days_ago = 7

target_date = start_date - timedelta(days = days_ago)

return target_date

print( datetime.today() )

print( get_previous_byday('Monday') )

print( get_previous_byday('Monday', datetime(2016, 8, 28)) )

第二种方法，用dateutil模块

Python代码

from datetime import datetime

from dateutil.relativedelta import relativedelta

from dateutil.rrule import *

d = datetime.now()

print(d)

print(d + relativedelta(weekday=FR))

print(d + relativedelta(weekday=FR(-1)))