今天：today = datetime.date.today()
昨天：yesterday = today - datetime.timedelta(days=1)
上个月：last_month = today.month - 1 if today.month - 1 else 12
当前时间戳：time_stamp = time.time()
各种类型的转换
时间戳转datetime：datetime.datetime.fromtimestamp(time_stamp)
datetime转时间戳：int(time.mktime(today.timetuple()))
datetime转字符串：today_str = today.strftime("%Y-%m-%d")
字符串转datetime：today = datetime.datetime.strptime(today_str,"%Y-%m-%d")
补时差：today + datetime.timedelta(hours=8)