两篇值得看的博客：
https://www.cnblogs.com/huigebj/p/11259449.html
https://blog.csdn.net/zzddada/article/details/102822337
from datetime import datetime
setTime = ‘2015-04-16‘
now = datetime.strptime(setTime, "%Y-%m-%d")
from datetime import timedelta
delta = datetime.timdelta(days=1) # 用来做加减日期
now.strptime("%Y-%m-%d")
原文：https://www.cnblogs.com/catfish1921/p/15229217.html