第一种方法：  
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
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)))