python datetime获取当前时间（天、月、年）以及昨天、上月、上一年
import datetime today = datetime.datetime.now().day yesterday = (datetime.datetime.now() - datetime.timedelta(days=1)).day hour = datetime.datetime.now().hour last_hour = (datetime.datetime.now() - datetime.timedelta(minutes=60)).hour month = datetime.datetime.now().replace(day=1).month last_month = (datetime.datetime.now().replace(day=1) - datetime.timedelta(days=1)).month year = datetime.datetime.now().year last_year = (datetime.datetime.now() - datetime.timedelta(days=365)).year
时间不能直接加减，需要用到 datetime.timedelta() 函数
