21.获取周几

import datetime

num = 5

date = (datetime.datetime.now() - datetime.timedelta(days=num)).strftime('%Y-%m-%d') 
print date

week = datetime.datetime.strptime(date.replace('-', ''), '%Y%m%d').weekday()
print week
if week == 6:
    print '周日'
    print (datetime.datetime.strptime(date.replace('-', ''), '%Y%m%d')- datetime.timedelta(days=2)).strftime('%Y-%m-%d')
elif week == 5:
    print '周六'
    print (datetime.datetime.strptime(date.replace('-', ''), '%Y%m%d')- datetime.timedelta(days=1)).strftime('%Y-%m-%d')

返回的week是int类型，0-6分别对应周一到周日，如果是周六或者周日就取周五的时间