time模块与datetime模块，字符串与日期类型转换

dd = '2019-03-17 11:00:00'
dd = datetime.datetime.strptime(dd, "%Y-%m-%d %H:%M:%S")

dc = dd.strftime("%Y-%m-%d %H:%M:%S")

isinstance(now, datetime.datetime)

import time
import datetime
#先获得时间数组格式的日期
threeDayAgo = (datetime.datetime.now() + datetime.timedelta(days = 3))
#转换为时间戳:
timeStamp = int(time.mktime(threeDayAgo.timetuple()))
#转换为其他字符串格式:
otherStyleTime = threeDayAgo.strftime("%Y-%m-%d %H:%M:%S")

# 这个包可以传参数年月日都可以
from datetime import datetime
now_time = datetime.now()
#先安装这个包
# pip install python-dateutil
from dateutil.relativedelta import relativedelta as rd
result_date = now_time - rd(years=1)

import time,datetime
# 字符串-->时间元组-->时间戳
# 字符串：
str_date = "2021-06-30"
# 时间元组 = fun(字符串)
arr_date = time.strptime(str_date,"%Y-%m-%d")
# 时间戳 = fun(时间元组)
nums_date = int(time.mktime(arr_date))#默认是float


import time,datetime
# 时间戳-->时间元组-->字符串
#1.获取时间戳
nums_date = time.time()
# 2.时间元组 = fun(时间戳)
arr_date = time.localtime(nums_date)
#3.字符串 = fun(时间元组)
str_date = time.strftime("%Y-%m-%d", arr_date)

"%Y-%m-%d %H:%M:%S"