Python日期的加减

https://segmentfault.com/q/1010000012025203

对于天，小时，分钟和秒的加减使用timedelta就可以做到

from datetime import datetime,timedelta
yesterday = datetime.now() + timedelta(days=-1,hours=-1,minutes=-1,seconds=-1)

但是对于月的加减就需要用到下边的方式

from dateutil.relativedelta import relativedelta
last_month = datetime.now() + relativedelta(months=-1)