datetime.datetime.now() 

datetime.timedelta(参数=数值)  #参数：weeks，days，hours，minutes，seconds，microseconds，milliseconds

import datetime

nowtime = datetime.datetime.now()

print(nowtime) #当前时间

print(datetime.datetime.now() - datetime.timedelta(days=1)) #1天前 默认格式2019-02-11 13:27:16.231381

print(datetime.datetime.now() + datetime.timedelta(days=1)) #1天后

print((datetime.datetime.now() - datetime.timedelta(weeks=2)).strftime("%Y-%m-%d %H:%M:%S")) #两周前

print((datetime.datetime.now() + datetime.timedelta(weeks=2)).strftime("%Y-%m-%d %H:%M:%S")) #两周后

print((datetime.datetime.now() - datetime.timedelta(days=1)).strftime("%Y-%m-%d %H:%M:%S")) #1天前

print((datetime.datetime.now() + datetime.timedelta(days=1)).strftime("%Y-%m-%d %H:%M:%S"))#1天后

print((datetime.datetime.now() - datetime.timedelta(hours=2)).strftime("%Y-%m-%d %H:%M:%S")) #2小时前

print((datetime.datetime.now() + datetime.timedelta(hours=2)).strftime("%Y-%m-%d %H:%M:%S")) #2小时后

print((datetime.datetime.now() - datetime.timedelta(minutes=30)).strftime("%Y-%m-%d %H:%M:%S"))# 30分钟前

print((datetime.datetime.now() + datetime.timedelta(minutes=30)).strftime("%Y-%m-%d %H:%M:%S")) #30分钟后

print((datetime.datetime.now() - datetime.timedelta(seconds=10)).strftime("%Y-%m-%d %H:%M:%S")) #10秒前

print((datetime.datetime.now() + datetime.timedelta(seconds=10)).strftime("%Y-%m-%d %H:%M:%S")) #10秒后