python 中time, datetime的用法

1. time

• 第一种是时间戳的方式(相对于1970.1.1 00:00:00以秒计算的偏移量),时间戳是惟一的

　　time.time()

• 第二种以数组的形式表示即(struct_time),共有九个元素，分别表示，同一个时间戳的struct_time会因为时区不同而不同

　　time.localtime()

• gmtime()与mktime（）可以将两种时间表示方法自由转换

>>> time.gmtime(time.time())
time.struct_time(tm_year=2016, tm_mon=5, tm_mday=24, tm_hour=9, tm_min=15, tm_sec=12, tm_wday=1, tm_yday=145, tm_isdst=0)
>>> time.mktime(time.localtime())
1464081346.0

• strftime 和strptime

>>> time.strftime("%Y%m%d", time.localtime())
‘20160524‘
>>> time.strptime(‘20160524‘, "%Y%m%d")
time.struct_time(tm_year=2016, tm_mon=5, tm_mday=24, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=1, tm_yday=145, tm_isdst=-1)

2. datetime

>>> datetime.datetime.now()
datetime.datetime(2016, 5, 24, 17, 35, 10, 553391)
>>> datetime.datetime.now().strftime("%Y%m%d_%H%M%S")
‘20160524_173543‘

可以对时间进行比较

>>> time1 = datetime.datetime.now()
>>> time2 = datetime.datetime.now()
>>> time2 -time1
datetime.timedelta(0, 5, 944002)
>>> time2 > time1
True
>>> datetime.datetime.now() - datetime.timedelta(days = 2)
datetime.datetime(2016, 5, 22, 17, 38, 57, 994761)

3. time ---> datetime

>>> datetime.datetime.fromtimestamp(time.time())
datetime.datetime(2016, 5, 24, 17, 40, 44, 138647)