datetime.datetime类介绍

datetime类是date和time的结合体，包括date与time的所有信息，date和time类中具有的方法和属性，datetime类都具有。


所以在我们日常的工作中，可以仅使用datetime类。该类的构造函数： 
datetime.datetime(year, month, day[, hour[, minute[, second[, microsecond[,tzinfo]]]]]) 
各参数的含义与date、time构造函数中的一样，但是要注意各参数的取值范围。 




1、today函数  返回一个当前本地时间的datetime.datetime类的对象。
2、now（[tz]) 不指定时区，返回一个当前本地时间的datetime.datetime类的对象。指定时区，返回指定时区的时间
3、fromtimestamp(timestamp[,tz]) 给定一个时间戳，返回指定时区的datetime.datetime类的对象。不指定时区，返回本地时区的datetime类对象
4、strptime("时间字符串",format) 将格式时间字符串转换为datetime对象
5、Datetime类—year、month、day、hour、minute、second属性 






>>> import datetime
>>> datetime.datetime.today()
datetime.datetime(2018, 1, 17, 21, 8, 41, 964000)
>>> print datetime.datetime.today()
2018-01-17 21:08:55.260000
>>> print datetime.date.today()
2018-01-17
>>> print datetime.datetime.now()
2018-01-17 21:09:15.708000
>>> import time
>>> print datetime.datetime.fromtimestamp(time.time())
2018-01-17 21:10:22.618000
>>> time.now()
Traceback (most recent call last):
  File "", line 1, in
AttributeError: 'module' object has no attribute 'now'
>>> print datetime.datetime.strptime("2018-01-16 23:44:55","%Y-%m-%d %H:%M:%S")
2018-01-16 23:44:55
>>> datetime.datetime.strptime("2018-01-16 23:44:55","%Y-%m-%d %H:%M:%S")
datetime.datetime(2018, 1, 16, 23, 44, 55)
>>> tm3=datetime.datetime.strptime("2018-01-16 23:44:55","%Y-%m-%d %H:%M:%S")
>>> tm3.year
2018
>>> tm3.day
16
>>> tm3.month
1
>>> tm3.hour
23
>>> tm3.minute
44
>>> tm3.second
55
>>> tm3
datetime.datetime(2018, 1, 16, 23, 44, 55)
>>> tm3.microsecond
0
>>>




6、datetime.date() 参数是datetime.datetime类的对象，得到一个datetime.date对象
7、datetime.time() 参数是datetime.datetime类的对象，得到一个datetime.time对象
8、datetime.combime() 参数是datetime.datetime类的对象、datetime.date对象、datetime.time对象，得到一个datetime.datetime对象




>>> datetime.datetime.date(datetime.datetime.today())
datetime.date(2018, 1, 17)
>>> datetime.datetime.time(datetime.datetime.today())
datetime.time(21, 25, 16, 365000)


>>> datetime.datetime.combine(datetime.datetime.today(),datetime.time(10,34,55))


datetime.datetime(2018, 1, 17, 10, 34, 55)
>>> datetime.datetime.combine(datetime.date(2016,4,6),datetime.time(10,10,10))
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>>


9、datetime.replace([year[, month[, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]]]]]) 函数


>>> tm4=datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm5= tm4.replace(year=2018)
>>> tm5
datetime.datetime(2018, 4, 6, 10, 10, 10)
>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>>


10、datetime.timetuple()函数：得到一个time.struct_time对象


>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm4.timetuple()
time.struct_time(tm_year=2016, tm_mon=4, tm_mday=6, tm_hour=10, tm_min=10, tm_se
c=10, tm_wday=2, tm_yday=97, tm_isdst=-1)
>>> tm5=tm4.timetuple()
>>> print tm5
time.struct_time(tm_year=2016, tm_mon=4, tm_mday=6, tm_hour=10, tm_min=10, tm_se
c=10, tm_wday=2, tm_yday=97, tm_isdst=-1)
>>> time.mktime(tm5)
1459908610.0
>>>


11、datetime.weekday(time)函数  参数time是一个datetime.date类型或datetime.datetime类型的数据。返回weekday中的星期几，星期一，返回0；星期二，返回1；以此类推。 


以下可以看出，参数只能是datetime.datetime类的对象或datetime.date类的对象


>>> tm5
time.struct_time(tm_year=2016, tm_mon=4, tm_mday=6, tm_hour=10, tm_min=10, tm_se
c=10, tm_wday=2, tm_yday=97, tm_isdst=-1)
>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm3=datetime.date.today()
>>> tm3
datetime.date(2018, 1, 17)
>>> datetime.datetime.weekday(tm5)
Traceback (most recent call last):
  File "", line 1, in
TypeError: descriptor 'weekday' requires a 'datetime.date' object but received a
 'time.struct_time'
>>> datetime.datetime.weekday(tm3)
2
>>> datetime.datetime.weekday(tm4)
2
>>>




12、datetime.isocalendar(time)函数  参数time是一个datetime.date类型或datetime.datetime类型的数据。返回元组(year,month,day)


>>> tm5
time.struct_time(tm_year=2016, tm_mon=4, tm_mday=6, tm_hour=10, tm_min=10, tm_se
c=10, tm_wday=2, tm_yday=97, tm_isdst=-1)
>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm3=datetime.date.today()
>>> tm3
datetime.date(2018, 1, 17)
>>> datetime.datetime.isocalendar(tm5)
Traceback (most recent call last):
  File "", line 1, in
TypeError: descriptor 'isocalendar' requires a 'datetime.date' object but receiv
ed a 'time.struct_time'
>>> datetime.datetime.isocalendar(tm4)
(2016, 14, 3)
>>> datetime.datetime.isocalendar(tm3)
(2018, 3, 3)
>>> type(datetime.datetime.isocalendar(tm3))

>>>


13、datetime.strftime(format)函数  返回自定义的格式时间字符串。参数format是自定义的时间格式。 


>>> tm4
datetime.datetime(2016, 4, 6, 10, 10, 10)
>>> tm4.strftime("%Y-%m-%d %H:%M:%S")
'2016-04-06 10:10:10'
>>>