Python之基本的日期与时间转换 datetime、 dateutil模块

简单举例datetime模块

from datetime import timedelta,datetime
a = timedelta(days=2, hours=6)
b = timedelta(hours=4.5)
c=a+b
print(c)  # 2 days, 10:30:00
print(c.seconds)  #
print(c.seconds/3600)  # 10.5
print(c.total_seconds())  # 210600.0

表示指定的日期和时间

d=datetime(2018,2,4)
print(d)  # 2018-02-04 00:00:00
print(d+timedelta(days=5))  # 2018-02-09 00:00:00
e=datetime(2018,3,4)
print(e-d)  # 28 days, 0:00:00

# datetime 会自动处理闰年
print((e-d).days)  #

需要执行更加复杂的日期操作，比如处理时区，模糊时间范围，节假日计算等等， 可以考虑使用 dateutil模块

f= datetime(2019, 1, 23)
# print(f+timedelta(months=1))  # 'months' is an invalid keyword argument for this function
from dateutil.relativedelta import relativedelta
print(f+relativedelta(months=+1))  # 2019-02-23 00:00:00

# dateutil.relativedelta() 函数有一点需要注意的就是，它会在处理月份(还有它们的天数差距)的时候填充间隙
aa=datetime(2019,2,1)
bb=datetime(2019,4,5)
print(bb-aa)  # 63 days, 0:00:00
cc=relativedelta(bb,aa)
print(cc)   # relativedelta(months=+2, days=+4)
print(cc.months)  #
print(cc.days)  #

题目：计算最后一个周日的日期

通用解答：

from datetime import datetime, timedelta

weekdays = ['Monday', 'Tuesday', 'Wednesday', 'Thursday',
            'Friday', 'Saturday', 'Sunday']

def get_previous_byday(dayname, start_date=None):
    """
    Topic: 最后的周日
    Desc :

    """
    if start_date is None:
        start_date = datetime.today()
    day_num = start_date.weekday()  # 开始日期
    day_num_target = weekdays.index(dayname)  # 目标日期，星期一索引为0
    print(day_num,day_num_target)  # 4 6/0 6/4,6
    days_ago = (7 + day_num - day_num_target) % 7
    print(days_ago)  # 5/1/5
    if days_ago == 0:
        days_ago = 7
    target_date = start_date - timedelta(days=days_ago)
    return target_date

target_date=get_previous_byday('Sunday', datetime(2012, 12, 21))  # 星期日
target_date=get_previous_byday('Sunday')  # 2019-03-03 16:34:01.143620
target_date=get_previous_byday('Sunday',datetime(2019, 3, 1))  # 2019-02-24 00:00:00

print(target_date)

 如果你要像这样执行大量的日期计算的话，你最好安装第三方包 python-dateutil 来代替

from dateutil.relativedelta import relativedelta
from dateutil.rrule import *
date=datetime.now()
# Next Friday
print(date+relativedelta(weekday=FR))  # 2019-03-08 17:29:57.376490
# Last Friday
print(date+relativedelta(weekday=FR(-1)))  # 2019-03-01 17:30:44.357886