python时间模块-time和datetime

python 中时间表示方法有：时间戳，即从1975年1月1日00:00:00到现在的秒数；格式化后的时间字符串；时间struct_time 元组。
struct_time元组中元素主要包括tm_year（年）、tm_mon（月）、tm_mday（日）、tm_hour（时）、tm_min（分）、tm_sec（秒）、tm_wday（weekday0 - 6（0表示周日））、tm_yday（一年中的第几天1 - 366）、tm_isdst（是否是夏令时
1. time
常用函数
time.time() 返回当前时间戳

>>> time.time()
1465370844.096474

time.ctime() 返回这种格式的时间字符’Wed Jun 8 15:27:48 2016’，显示当前时间.同时也可以转换时间戳

>>> time.ctime()
Wed Aug 22 17:47:31 2018'

>>> time.ctime(time.time()-86400)
'Tue Aug 21 17:50:07 2018'

time.localtime将时间戳转换成struct_time格式

>>> time.localtime()
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=17, tm_min=47, tm_sec=44, tm_wday=2, tm_yday=234, tm_isdst=0)

time.mktime 将struct_time格式转回成时间戳

>>> now = time.localtime()
>>> now
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=17, tm_min=54, tm_sec=51, tm_wday=2, tm_yday=234, tm_isdst=0)
>>> time.mktime(now)
1534931691.0

time.strftime 将struct_time格式转成指定的字符串格式

>>> now = time.localtime()
>>> now
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=18, tm_min=0, tm_sec=20, tm_wday=2, tm_yday=234, tm_isdst=0)
>>> time.strftime("%Y-%m-%d %H:%M:%S",now)
'2018-08-22 18:00:20'

time.strptime 将自定义时间格式的字符串转换为struct_time格式

>>> time.strptime("2018-08-22","%Y-%m-%d")
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=2, tm_yday=234, tm_isdst=-1)
>>> time.strptime("2018-08-22 18:03:30", "%Y-%m-%d %H:%M:%S")
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=18, tm_min=3, tm_sec=30, tm_wday=2, tm_yday=234, tm_isdst=-1)

1. datetime
   datime是time的升级版，可以对date(日期)、time(时间)、datetime（日期时间）等三种单独管理。主要是由下面四个类组成
   datetime.datetime常用函数（datetime.date datetime.time通用）

＃datetime.datetime.today() 默认返回当前日期和时间的对象，也可以自定义日期和时间

>>> import datetime
>>> today = datetime.datetime.today()
>>> print today
2018-08-22 18:12:14.568491
>>> last = datetime.datetime(2018,8,22,18,12,14)  ＃注意此处表示日期只能是实际月份，不能带0
>>> print last
2018-08-22 18:12:14

>>> last = datetime.datetime(2018,08,22,18,12,14)
File "<input>", line 1
last = datetime.datetime(2018,08,22,18,12,14)
^
SyntaxError: invalid token

#datetime.datetime.now() 返回当前时间
>>> datetime.datetime.now()
datetime.datetime(2018, 8, 22, 18, 16, 16, 660619)

＃ datetime.strftime(format)  ＃自定义格式化时间
>>> today.strftime("%I:%M:%S %p %d/%m/%Y")
'06:12:14 PM 22/08/2018'

＃ datetime.datetime.timple() 将时间转换为struct_time 格式
>>>today.timetuple()
time.struct_time(tm_year=2018, tm_mon=8, tm_mday=22, tm_hour=18, tm_min=12, tm_sec=14, tm_wday=2, tm_yday=234, tm_isdst=-1)

＃datetime.replace（）返回一个替换后的date对象
>>>last = today.replace(1949,10,1)
>>> print last
1949-10-01 18:12:14.568491
>>> last = today.replace(year=1919,month=3,day=2)
>>> print last
1919-03-02 18:12:14.568491

# datetime.datetime.strptime  将字符串转换为日志格式对象
>>> a = a = "2018-08-22 18:25:19"
>>> b = datetime.datetime.strptime(a,"%Y-%m-%d %H:%M:%S")
>>> print(a)
2018-08-22 18:25:19
>>> print(b)
2018-08-22 18:25:19
>>> print(type(a))
<class 'str'>
>>> print(type(b))
<class 'datetime.datetime'>

datetime.timedelta 时间运算
可用参数：days seconds microseconds milliseconds minutes hours weeks

today = datetime.datetime.now()
>>> print(today)
2018-08-22 18:26:20.360822
>>> yesterday = today - datetime.timedelta(days=1)
>>> print(yesterday)
2018-08-21 18:26:20.360822
>>> last_hour = today - datetime.timedelta(hours=1)
>>> print(last_hour)
2018-08-22 17:26:20.360822